Obama has named Merrick Garland to replace Antonin Scalia on the Supreme Court. He's a moderate, and not that young, and he has been praised in the past by Senate Republicans. Between the choice of Garland and Trump, Republicans are now in a no-win situation.
When Antonin Scalia died and Mitch McConnell immediately announced that the Republicans would prevent Obama from filling the vacancy, I posted this about McConnell's gambit.
The basic problem is this: fear of a conservative revolt means McConnell can't allow a Democrat to fill any important court vacancies. But, McConnell must know that Democrats can't cede complete control of the Judiciary branch to the Republicans. The eventual solution? Then end of advice and consent.
McConnell is now trapped. He can't back out of his pledge to block Obama's nomination. However, things are now looking pretty good for Hillary. Why? Trump is the nominee, and conventional wisdom right now is that Trump is a weak general election candidate. We shouldn't be too hasty in discounting Trump, as I will discuss later, but if McConnell buys conventional wisdom here, he is trapped. Either he backs down on Garland, or Hillary names someone way to Garland's left. What happens then depends on whether or not Trump drags the Senate down with him, giving the Democrats control.
Let's say Republicans keep the Senate. McConnell won't be able to claim that the nomination was too close to an election. It will be literally the first thing Hillary does. It will be as far from an election as mathematically possible. And Hillary will claim that by McConnell's own reasoning, the people will have spoken, and the Senate should abide. What then? McConnell is trapped. He won't be able to let the confirmation go through without be sacked by conservatives in his own party, and he won't be able to block the nominee without pushing things further towards crisis.
Or, let's say Trump drags down the whole party, and Democrats get the Senate. By blocking Garland, the Senate will have ensured the seat going to someone far more liberal.
What happens now? It depends on whether McConnell wants to bury his head in the sand and hope that November gives him an out, or whether he can think of something I haven't.
One way or another, advice and consent won't last. A system in which one party is disallowed from filling judicial vacancies is not sustainable, and McConnell knows that.