I'm pretty sure the Republicans think they have the political capital to not act on any nomination before the election (and then before the end of Obama's term).
Since they control the Senate, they can slow down the process to a crawl, but still move it along, and then just have a vote at the end which the nominee loses, and then the process starts over. I think it's the right thing to do, although it does depend on Obama's choice. If he chooses somebody middle of the road, who is willing to uphold the recent decisions on Citizens United, gun rights, etc., (even including same sex marriage), I think the Senate might approve. It might even be the smart thing for Obama to do. I haven't thought it through yet.
If Obama really wanted to throw Republicans for a loop, he would nominate
Maryanne Trump Barry. She's actually pretty liberal, but the Republicans' likely nominee isn't going to oppose her nomination.