What does the November election have in store for us? Well, given the fact that Obama has yet to show a clear lead in the polls, 10 months out this race is too close for my comfort.
I'm going to work from national polls, because until the GOoPers have a nominee we won't see any state-by-state results.
Obama won in 2008 with 52.9% of the popular vote. Let's start there. No sitting President who has won re-election has ever seen his popular vote share decrease (ignoring the outliers of FDR's 3rd and 4th terms).
The polls have Obama well below this, so we do have so cause for concern.
Barring a massive drop in unemployment this year or Romney/Gingrich sticking their foot in their mouth so far they can feel intestines, 55% would be Obama's ceiling (LBJ and FDR are the only Democrats to have ever topped this).
A slight drop to 52% would be more what I expect. The question is more of what is the GOP's floor? My guess is in the 39-43% range (or Obama minus 10-16%) with a lot of otherwise GOP votes going third party because they won't be able to stomach voting for either Obama or whichever incompetent boob wins their nominating process.
Historically the best finishes by Democrats in the two-party era have been:
1. FDR 1936 +24.3% (he also holds 4th, 5th, and 7th)
2. LBJ 1964 +22.6%
3. Wilson 1912 +18.6%
At this point I think we can safely rule an Obama re-elect margin like that out unless we see a third party run (Paul, Trump, Johnson) that gets a good head of steam going.
Let's examine that GOP floor because that floor matters since each percentage translates into electoral votes.
537-1: For an Obama clean sweep the GOP nominee would have to poll nationally around Obama minus 40% to give up the one vote in NE3. No major party candidate has ever lost by more than 26.2% (James Cox-D 1920). Romney is the only one of the GOP's current Top 4 who could conceivablly drop that low because who knows what gaffe he'll pull to push people to third parties, but if that were the case I'd expect a conservative third party candidate to win this district before Obama. (By contrast a Democratic nominee would have to be polling below 20% nationally for the loss of DC and its 3 votes to be even be conceivable)
525-13: At –33% Wyoming and its 3 votes come into play, at –29% OK (7) and UT (6) come into play. Ron Paul's floor is somewhere in this neighborhood, simply because I think national security voters would hold their nose and vote Obama before voting Paul, and liberals who are supporting Paul in the GOP primaries would come home rather than vote for a racist homophobe.
503-35: At –25% ID (4), at –23% AK (3), and at –21% AL (9) and AR (6) come into play. –21% is Santorum's floor. By contrast a Democratic nominee polling at -21% is going to win DC plus a mere one other state, see Mondale and McGovern.
469-69: At -15% KY (8), NE*+NE1 (3), KS (6), TN (11), WV (5), and MS (6) all come into play. This is Newt Gingrich's floor, but it's also Herbert Hoover territory.
416-122: Realistically it's hard to see the GOP nominee dropping below -11% no matter which clown they nominate, barring some monumental scandal or third partier with momentum (see Wilson vs Roosevelt+Taft), thus adding TX (38), ND (3), SD (3), and SC (9) to the totals. But I also think this is Ron Paul's ceiling.
376-168: At -7% we're eking back into McCain territory putting AZ (11), GA (16), MT (3), and MO (10) into play. But I also think this is Santorum's ceiling, I just can't see the hateful loser doing better than this.
343-195: If the GOP clown nominee starts polling at Obama-5% then NC (15), IN (11), and NE2 (1) will fall. But I also think this is Gingrich's ceiling, I really don't see Americans who give Congress 9% popularity, who dislike cheaters, and hate lobbyists could pull the lever for Gingrich.
283-255: If the GOP clown nominee gets to -2% I start to sweat as FL (29), OH (18), and VA (13) could all fall.
270 even: At ±1% we're in a tie as CO (9) and IA (6) fall to even things up.
235-305: At +2% Romney pulls ME2 (1), MN (10), NH (4), and PA (20) to win. This is also his ceiling, though realistically I don't see how he gets close to this once voters get engaged in September because there aren't enough racists and 1%ers to make up for the evangelicals and working-class folks who will look elsewhere, unless unemployment inexplicably moves up.
227-313: And frankly I can't see any miracle that is going to land in the GOP's lap that would push any more states in their column. The remaining states are far too blue. The ones closest to a bubble that a Carter-like +9% margin would bring into play, like Nevada (couldn't vote GOP even in 2010) and Wisconsin (energized, anti-GOP) aren't going to switch parties this year. Maybe ME+ME1 (3) and NM (5) could reach this spot. But it's just not likely.