Mississippi: Polls close at 8 PM ET. Note that for any races in which no one wins more than 50 percent, a runoff will be held June 24.
• MS-Sen (R): Republican Sen. Thad Cochran's long tenure and occasional bipartisan actions have earned him the ire of many anti-establishment conservatives. They are backing state Sen. Chris McDaniel, who is depicting himself as a tea party champion. Cochran and own well-funded allies are hitting back, portraying Cochran's seniority as an asset and accusing McDaniel as not being as ideologically pure as he claims.
The already heated race took a very nasty turn in the final weeks after a pro-McDaniel blogger broke into the nursing home where Cochran's wife is a patient and illegally recorded her. While McDaniel's campaign has been criticized over the incident (there's no sign they were directly involved) Cochran hasn't emerged unscathed either: His campaign apparently knew about the break-in before the police but sat on the evidence for two weeks.
What limited polling there is indicates that the incident hasn't destroyed either candidate's chances, and the race looks close. It's possible that neither candidate will have enough on Tuesday to win outright, forcing them into a runoff three weeks later. The eventual winner will face former Democratic Rep. Travis Childers, who may have a chance against McDaniel.
• MS-04 (R): Republican Rep. Steven Palazzo unseated longtime conservative Democratic Rep. Gene Taylor in 2010. Taylor is seeking to avenge his loss, but this time he is running for this red Gulf Coast seat as a Republican. While Taylor earned a great deal of respect during his tenure, this looks like a very uphill climb for him. Palazzo has outspent Taylor $311,000 to $121,000 in the final months of the race and he has the state Republican establishment behind him. It's also hard to see Republican primary voters embracing a longtime Democrat. A few minor Republicans are running, so it's possible for this to go to a runoff.
Head over the fold for more races to watch on Tuesday.
Alabama: Polls close at 8 PM ET. Note that for any races where no one wins more than 50 percent, a runoff will be held July 15.
• AL-06 (R): With powerful Rep. Spencer Bachus retiring, seven Republicans are competing to replace him in one of the country's most conservative seats. Corporate executive Will Brooke has spent the most money in the last few months, with state Rep. Paul DeMarco also spending big; tea-partying surgeon Chad Mathis and think tank president Gary Palmer have also spent over $250,000 in the home stretch. Three other Republicans, including state Sen. Scott Beason, are in the race as well, but they haven't raised or spent much. The Club for Growth has also gotten involved, endorsing Mathis and hitting Brooke. DeMarco is reportedly ahead in the polls, but with so many candidates in this Birmingham-area seat, it's all but assured this will got to a July 15 runoff.
New Jersey: Polls close at 8 PM ET.
• NJ-03 (R): Two Republicans are dueling to succeed Rep. Jon Runyan in this South Jersey swing seat. Wealthy businessman Tom MacArthur, a former mayor of Randolph, is the Republican establishment's preferred choice. He faces former Bogota mayor and 2013 U.S. Senate nominee Steve Lonegan, who has a reputation as a loose cannon. Democrats would love to face Lonegan, and have even taken some steps to prop him up in the primary. However, MacArthur has outspent Lonegan $964,000 to $435,000, and recent polls show him favored to win. Obama won this seat 52/47 percent and the Republican nominee will face a credible challenge from Democratic Burlington County Freeholder Aimee Belgard.
• NJ-12 (D): Democratic Rep. Rush Holt leaves behind a safely blue seat located in the middle of the state, and three credible Democrats are hoping to claim it. A recent poll shows a tight race between state Sen. Linda Greenstein and Assemblywoman Bonnie Watson Coleman, with Assemblyman Upendra Chivukula further back. However, Chivukula has spent more in the home stretch than his opponents and Greenstein's fundraising has been weak, so it looks like any of the three legislators can take this.
South Dakota: Polls close at 8 PM ET (Central time zone) and 9 PM ET (Mountain time zone). Note that in races in which no one wins more than 35 percent, a runoff will be held August 12.
• SD-Sen (R): Republicans have an excellent chance to pick up retiring Democratic Sen. Tim Johnson's seat in this red state. Five Republicans are running, and former Gov. Mike Rounds is the clear front-runner. Some outside conservative groups initially hoped to oppose Rounds, but none of them got involved in any meaningful way. Rounds' primary foes has not distinguished themselves much either, and it looks like he should win the nomination without much trouble. The Republican nominee will be the clear favorite against former Democratic Congressional aide Rick Weiland, though the independent campaigns of former Sen. Larry Pressler and former state Sen. Gordon Howie (both former Republicans) do complicate things.
New Mexico: Polls close at 9 PM ET.
• NM-Gov (D): Republican Gov. Susana Martinez is favored to win a second term but is not assured victory, and five Democrats are hoping she isn't as strong as she seems. State Attorney General Gary King, son of former Gov. Bruce King, started the race as the best-known candidate. However, King hasn't raised or spent much money and looks vulnerable to an upset. Businessmen Lawrence Rael and Alan Webber, and state Sens. Howie Morales and Linda Lopez are hoping they can pull of a surprise on Tuesday. A recent poll gave King 22 percent, with Rael and Webber at 16 and a ton of undecideds.
Iowa: Polls close at 10 PM ET. Note that in Republican primaries races in which no one wins more than 35 percent, the nomination will be decided at the June 14 state convention.
• IA-Sen (R): Democratic Sen. Tom Harkin is retiring and five Republicans are running to take his place. In recent weeks, state Sen. Joni Ernst has broken off from the pack and emerged as the front-runner. The Republican establishment has largely coalesced around Ernst, and she has benefited from outside group spending as well as her own very memorable ads. Ernst's main opponent looks like former wealthy businessman Mark Jacobs. Also in the race are former U.S. Attorney Matt Whitaker, radio host Sam Clovis and Some Dude Scott Schaben. The winner will face Democratic Rep. Bruce Braley.
• IA-01 (D & R): Five Democrats are running to succeed Braley in this northeastern Iowa seat. Recent polling from Loras College gives state representative and former Speaker Pat Murphy a clear lead, but there are no other public polls to confirm this. Also in the running are former state Sen. Swati Dandekar, state Rep. Anesa Kajtazovic, attorney Dave O'Brien and Cedar Rapids City Councilor Monica Vernon. In the last few months, Vernon has outspent her opponents, but Murphy and Dandekar are not too far behind.
The Republicans start out as the underdogs in this 56/43 Obama district, but they may have a shot here. Businessman Rod Blum looks like the front-runner over Marshalltown School Board member Gail Boliver and frequent candidate Steve Rathje.
• IA-02 (R): Democratic Rep. Dave Loebsack isn't high on many Republican target lists, but Team Red is hoping 2014 will be its lucky year. State Rep. Mark Lofgren faces former state Public Health Director Mariannette Miller-Meeks, with one Some Dude in the mix. Miller-Meeks was the GOP nominee in 2008 and 2010, losing to Loebsack 51/46 in the latter contest. Obama won this southeastern seat 56/43.
• IA-03 (R): Republican Rep. Tom Latham is departing and opening up this swing seat. Six Republicans are running: businessman Robert Cramer; Secretary of State Matt Schultz; businessman Monte Shaw; David Young, former chief of staff to Sen. Chuck Grassley; and state Sen. Brad Zaun. While Cramer has spent the most, there doesn't appear to be an obvious front-runner: It looks like a very strong possibility that the nomination will need to be decided at the Republican convention. Whoever wins will take on Democratic former state Sen. Staci Appel in this Des Moines-area district that Obama carried 51/47.
Montana: Polls close at 10 PM ET.
• MT-Sen (D & R): Appointed-Democratic Sen. John Walsh faces a tough challenge to keep his seat in November. However, Walsh looks like the clear favorite in the primary against former Lt. Gov. John Bohlinger and rancher Dirk Adams. On the Republican side, Rep. Steve Daines should have little difficulty against state Rep. Champ Edmunds.
• MT-AL (R): Five Republicans are running to take Daines' place in Montana's lone congressional district. State Sen. Matt Rosendale and former state Sen. Ryan Zinke have both spent over half-a-million dollars in the last months of the race and look like the front-runners. Former Senate Minority Leader Corey Stapleton has also spent six figures and may be able to pull it off. State Sen. Elsie Arntzen and tea partier Drew Turiano have far fewer resources and probably won't get very far. The winner will take on Democrat and former congressional aide John Lewis.
California: Polls close at 11 PM ET. Note that in California, all candidates run on the same ballot in what is known as a "top-two primary." The two candidates with the most votes advance to the November general election, regardless of party.
To help you follow along with the state's many House races, we've included interactive maps of California. Northern California is first, with Southern California just below.
• CA-07 (2): Freshman Democratic Rep. Ami Bera sits in a suburban Sacramento swing district and three Republicans are competing to take him on. Former Rep. Doug Ose is the establishment choice: Ose is wealthy and has a reputation as a moderate, and he would probably be Bera's toughest opponent. Democrats would prefer to face the more conservative Igor Birman, a former congressional aide. Birman has the support of Ron and Rand Paul and has worked to portray Ose as a liberal. However, Birman has spent only half as much money as Ose in the final stretch of the campaign, while Ose is backed by the deep-pocketed U.S. Chamber of Commerce. A third candidate, 2012 Senate nominee Elizabeth Emken, is seen as a long shot to win. What little publicly released polling there is points to Ose advancing to the general.
• CA-15 (2): Freshman Rep. Eric Swalwell faces a challenge from state Senate Majority Leader Ellen Corbett in this safely blue district in the eastern Bay Area. While Corbett is well-known, she has not raised much compared to Swalwell and has run a somewhat disorganized race. The incumbent also should benefit from President Obama's endorsement. A third candidate, Republican Hugh Bussell, is also running. Bussell won't win the seat, but if he can consolidate enough Republican support here he can place second and deny Corbett a spot in the general. That would be very good news to Swalwell, who would have no problem defeating Bussell in this 68/30 Obama seat.
• CA-17 (2): Rep. Mike Honda is facing a very well-funded challenge from fellow Democrat and former Commerce Department official Ro Khanna. Khanna is arguing that the Silicon Valley-area district deserves new leadership and that he is better equipped to represent the seat than Honda. For his part, Honda has the backing of President Obama and many progressive organizations, including Daily Kos. Two Republicans are running and they are expected to split the district's small conservative vote enough so that both Honda and Khanna will advance to November. However, a pro-Honda group has recently spent to try and help Republican Vanila Singh, and it's possible she could get the second-place spot and deny Khanna a place in the general.
• CA-21 (2): Freshman Republican Rep. David Valadao sits in a Central Valley seat that Obama won 55/44, but one in which Democratic turnout tends to plunge during non-presidential elections. John Hernandez, the Democrat whom Valadao easily beat in 2012, unfortunately is running again. Hernandez ran a close to non-existent campaign against Valadao last time and would probably forfeit the seat again if he makes it to the general. Luckily, Democrats have a much better option in former congressional aide Amanda Renteria. If Renteria advances, Democrats have a chance to unseat Valadao.
• CA-24 (2): Republicans have an outside shot at beating Democratic Rep. Lois Capps in this coastal seat that includes Santa Barbara and San Luis Obispo. It looks like a battle between Santa Barbara City Councilor Dale Francisco and businessman Justin Fareed to face her. However, Capps would probably rather face actor Chris Mitchum, whose conservative views probably won't play well in this 54/43 Obama seat.
• CA-25 (2): Republican Rep. Buck McKeon is calling it quits here. The front-runner to replace him looks like former Republican state Sen. Tony Strickland, who has a well-deserved reputation as a good fundraiser. Strickland's main inter-party opponent is state Sen. Steve Knight, who has raised very little. Democrat Lee Rogers, a podiatrist and the party's 2012 nominee, is likely to secure the other general election spot.
However, this area saw very weak primary turnout from Democrats in 2012 and there's a chance that it could be Strickland and Knight in the general instead. This seat, which includes Santa Clarita and Palmdale, leans Republican, but not overwhelmingly: Romney won 50/48 here and Rogers is well-funded enough that he could make things interesting.
• CA-31 (2): Republicans face an uphill climb to keep this 57/41 Obama seat, and Rep. Gary Miller's retirement does not make things easier for Team Red. However, it's far from clear which of the three Republicans and four Democrats running will advance to the general. Initially, it looked to be a competition between Redlands Mayor Pete Aguilar and attorney Eloise Reyes to be the Democratic contender, with Republican businessman Paul Chabot favored to meet one of them in November.
However, things have gotten far more complicated. Aguilar and Reyes have been attacking each other, and some Democrats are worried that Republican Lesli Gooch, a former congressional aide, could pull off a surprise and join Chabot in the general. A similar thing happened in this district in 2012: Miller and Republican Bob Dutton surprisingly got the most votes in June and voters had to choose between two Republicans in November even as they were decisively voting for Obama.
Former Rep. Joe Baca, a conservative Democrat who used to represent much of this seat, is also running. While Baca has raised very little money and has tended to make the news for all the wrong reasons, it's not out of the question that he could make it to the general. A lot can happen here and Democrats won't rest easy until it's clear that someone from Team Blue has made it past the top-two primary this time.
• CA-33 (2): Longtime Democratic Rep. Henry Waxman is retiring, leading to a chaotic battle to replace him. Obama won 61/37 here and 10 Democrats are running. Initially, this looked like a duel between state Sen. Ted Lieu and former Los Angeles Controller and 2013 mayoral runner-up Wendy Greuel to at least make it to the general. However, attorney David Kanuth and radio host Matt Miller, who like Greuel and Lieu are both Democrats, have each spent notable amounts of money.
Three Republicans are running, with veteran Elan Carr spending a credible amount of money. If Carr can consolidate enough of the district's Republican minority, he has a good shot at propelling himself into the general. Complicating things further is the presence of well-known author Marianne Williamson, running as a left-leaning independent. Williamson has spent heavily and it's possible she could grab one of the two general election spots. This is probably Tuesday's most unpredictable race and there's no telling which two candidates, or even which parties, will get enough votes on Tuesday to make it to the general.
• San Jose Mayor (2): America's 10th largest city will hold its non-partisan primary on Tuesday, with the top two vote-getters advancing to the general. San Jose is heavily Democratic and while all the major candidates identify as Democrats, there are real ideological divisions here. Most of the field is allied with outgoing Mayor Chuck Reed, whose pension policies have angered labor. The one labor ally is Santa Clara County Supervisor and 2006 mayoral candidate Dave Cortese.
Cortese is favored to advance to the general, but the second spot is more uncertain. Four city councilors are running, but it looks like Sam Liccardo and Vice Mayor Madison Nguyen are the most likely to make it to November. A recent SurveyUSA poll showed Cortese in first with Liccardo leading Nguyen 20/11 for second. However, that poll was conducted only in English and may have left out much of Nguyen's Vietnamese base. The primary has been a pretty clean affair, but things are expected to heat up once the field has been winnowed to two candidates.