The first reaction to Scalia's death from nearly everyone I know in political science was to declare with complete confidence that there is no chance of the Senate voting on a nominee until after the presidential election. Here I want to elaborate on why I think that is nonsense so that in a few months I can rub many faces in this.
One legitimate point in favor of the "no confirmation" argument is that the Republican Party of 2016 is completely unaffected by logic or historical precedent. The fact that no seat has sat vacant for 11+ months since the Civil War does not mean they won't leave a seat vacant for 11+ months, nor will the fact that their position makes no sense in either logical or practical terms get in their way. They are more than capable of and willing to do really stupid things.
My position is that Obama is going to nominate someone quickly and the Senate GOP's political capital will give out long before next February. The 2016 Senate races feature 7 incumbent Democrats running for re-election and a whopping 21 Republicans (leaving aside for a moment the open seats). These Republicans include many first-timers who got really lucky and won in a GOP wave election in 2010 and now face very long odds of getting re-elected. Republican Senate wins in places like Illinois, Wisconsin, and Pennsylvania – all of which the GOP won in 2010 with flat-out terrible candidates – are, if not flukes, at least veering uncomfortably close to fluke territory. Next, add in the open seats the GOP desperately wants (Florida, Nevada, etc) and it is clear that the balance of Senate control is very much at stake in this election. Republicans trying to hold or take seats in generally liberal or liberal-leaning states are going to sign their own electoral death warrant by taking the hard-line position on this. In states where people voted for Obama twice in substantial numbers, "I agree with Ted Cruz and Donald Trump on this vote" does not seem like a winning message.
In short, the GOP runs a very real and legitimate risk of having a delaying tactic blow up in their faces by pushing the vote back to early 2017 when the Senate could be controlled by Democrats. They're not great long-term thinkers, but certainly someone has to realize that this is a possibility. Since no one among the GOP higher-ups can have any illusions about how this presidential election is shaping up for them, the idea that they are on the cusp of taking control of the White House borders on hilarious. It is entirely possible that the Senate Republicans are dealing from their position of greatest strength right now and that their advantage will only erode the longer this drags on.
Were the party run by intelligent people they might understand that currently they could force at least some kind of concession from Obama in the form of a centrist New Democrat corporate type (as is widely rumored already). Given who this nominee replaces, even appointing that kind of jurist would represent a huge shift away from the right in the overall ideology of the court. And Republicans could at least draw comfort from the fact that this is precisely the type of "liberal" with a hard-on for corporate power who is likely to please them on some decisions.
The idea that waiting somehow improves their position is premised upon one or both of two propositions: that their Senate majority will increase or that they will take the White House. The former has the closest thing to 0% chance of happening that exists in the universe of this election. If anything, they are overwhelmingly likely to lose at least a couple seats (Mark Kirk is about as likely to win Illinois as I am) and possibly even to lose control of the chamber. If Trump wins their nomination, the consequences down-ballot for GOP House and Senate candidates could be dire. As for the latter, the odds of taking the White House – any objective analysis of the election as it unfolds would have to conclude that the Republicans have a chance greater than zero but it certainly is not looking likely right now. A more brutally honest view is that they have a terrible field of candidates, none of whom can even get the Republican primary electorate to get behind them, who would be a substantial underdog in the general election.
Finally, leaving the Court at 8 members for a year will create a ration of 4-4 votes wherein Scalia would have been the deciding 5th vote for the conservative bloc. Though such tie decisions do not establish precedent, they will affirm the (generally liberal) decisions of lower courts in a number of important pending or upcoming cases. This would at best set back by several years the conservative movement's efforts in a number of issue areas.
The fact that delaying the vote is stupid and ultimately likely to hurt the GOP far more than it helps them does not mean they will decline to do it. These are petulant people playing to an audience of morons. However, please keep in mind how often GOP Congressional Tough Talk actually gets backed up these days. Based on the recent past the more likely scenario is that they will threaten, showboat, whine, throw tantrums, and then eventually hold the vote anyway. Unless of course they shut down the government, which they totally swear they're really gonna do one of these times.