What are the risk/reward calculations apparently motivating Mitch McConnell’s actions? Here is my take ,,, and remember that the election is on 11/8/16, new Senators seated on 1/3/2017 and new President on 1/20/2017.
1) Merrick Garland is the absolute BEST selection that the GOP could ever hope for from President Obama (or any democrat). By taking his early stance opposing any vote McConnell pushed democrats into either selecting a centrist nominee whom might have a chance of being confirmed or a more progressive nominee whom would never be placed on the court by Republicans but might provide more energy and passion motivating democrats in the upcoming 2016.
2) He can always relent and allow a vote IF the winds turn and it looks like democrats will have a very strong hand after the election. So long as Garland’s nomination is not recalled by President Obama (or Garland) McConnell can relent and allow the vote at his choosing. This would eliminate the ability of a President Hillary Clinton (possibly with a solid democratic majority in the Senate) from nominating and putting on the Supreme Court a far more progressive judge. No fear on his end — if needed he can let the centrist judge be placed but can hold out for as long as it seems like he might get a Republican president.
3) Keeping the Supreme Court pick as an active part of the 2016 elections is a very effective way to get his base Republican voters to the poles. And here is the gold for him — even if Trump (or even Cruz) is the Republican nominee for President their FEAR of ‘losing’ the Supreme Court will have them hold their nose and still show up and vote. Plus hold their nose and get out and actively work to get Republicans elected. I can’t think of any other ‘fear’ that McConnell can inflame in the far right that would have as powerful an impact across the entire US than losing the Supreme Court. Conversely if he was to relent and allow the vote now these same base Republicans will feel truly betrayed and abandoned by the Republican party. What percentage would give up and not even bother to vote? Or actively act against the Republicans and support a third party?
4) The negative hit would be the pressure on ‘weak’ republican Senators up for reelection forming into the likelihood that they will lose their reelection and turn the Senate to democratic control. But with a Trump/Cruz at the head of the ticket isn’t that a likely result anyway — the loss of these seats to democrats? But as covered in #3 — keeping this issue as a 2016 campaign element probably provides the best option to turn out Republicans to keep some of those seats.
5) In the unlikely situation where Democrats win control of the Senate but lose the Presidency their is still the possibility of putting Garland on the Court. Since the Senators elected in 2016 take office at noon on the third day of January (1/3/2017) and the President on January 20 (1/20/2017) there are 17 days where the new Senate (under democratic control) can act PRIOR to the next president taking office. This would likely require the Senate to suspend the 60 vote filibuster rule for Supreme Court nominations (I assume dems will not hold 60 seats) and wade through republican obstructions and the normal time frame of 60-90 days to confirm. Not likely doable but a possibility.
So McConnell is in a lose — lose situation politically. However the least painful loss is to abandon his Constitutional responsibility of having the full Senate provide ‘advice and consent’ and reject having a vote on Garland (thus keeping the base engaged in the election). And ONLY relent after the election if the Senate and Presidency are taken by democrats. At that point allow a vote on the most centrist nominee the republicans could hope for. Do it in the 7 weeks after the election (while republicans still control the Senate) and prior to the new Democratic Senate taking office.
(update: David Nirr's article on Patty Davis challenging Chuck Grassley in 2016 opens the door that perhaps Grassley relents to try and save his personal senate seat. Grassley could be pressured to let Garland out of committee for a vote by the full Senate … but McConnell would still need to let it get to the floor and I still doubt that).