(Reuters/Brian Snyder)
Opinion writer

Why are incumbent Republican Senators who are facing difficult reelection challenges in states carried by Barack Obama refusing to even consider Obama’s nominee to the Supreme Court? It’s all about keeping the base happy.

But there’s a potential problem with this strategy: Donald Trump may blow it to pieces.

James Hohmann has some good reporting that clearly shows that keeping the base juiced up is the driving rationale behind refusing to even consider Merrick Garland. Senator Ron Johnson of Wisconsin — one of the most vulnerable GOP incumbents of the cycle — candidly confides to Hohmann that GOP base voters are more revved up over this battle than any other voters are, because they want to prevent the Court from tilting in a liberal direction, and that this is weighing on him. Hohmann concludes that even if independents and moderates might be disturbed by the GOP refusal to consider Garland, this probably won’t matter to GOP Senators, because Republican base voters are the most energized by the standoff:

With the exception of Illinois, where Sen. Mark Kirk has already been privately written off by almost all of his Republican colleagues, members in states like New Hampshire, Pennsylvania and Ohio are making plain they won’t ultimately confirm Garland (even if they agree to sit down with him for a photo opp). Though their electorates overall may lean Democratic, each believes their priority – especially at this point in the cycle – must be keeping the base ginned up.

It seems inarguable that this is what is driving the GOP position in this fight, which means the larger point here is that Mitch McConnell’s strategy of refusing to consider Garland is all about preserving the GOP Senate majority, and that he has decided the base is crucial to that.

But even if this is the most reasonable political calculation Republicans could make under the circumstances, one Democrat points out to me that these carefully laid plans could end up getting ruptured to an untold degree by Trump. After all, if Trump wins the nomination, a nontrivial percentage of Republican voters could stay home, perhaps even in some of these swing states where control of the Senate will be decided: Wisconsin, Ohio, Pennsylvania, New Hampshire, and Florida.

Indeed, while Democrats believe all of this to be very possible, this isn’t even a partisan line of speculation: Republicans themselves are worried that Trump could have this down-ticket impact if he is the nominee. One top GOP fundraiser told the Post that this dynamic could put GOP control of the Senate at risk: “If Donald Trump is the nominee, we could see a lot of people staying home.”

Meanwhile, National Journal’s Josh Kraushaar reported recently that GOP strategists are “privately alarmed but publicly silent at the prospect of Trump making life miserable for swing-state senators,” adding that Trump could produce “depressed Republican turnout” that could compound their problems.

And conservative writer Noah Rothman today highlighted a striking finding in a new Monmouth poll that also hints at this possibility:

In the Republican contest, two-thirds (68%) of voters who back Ted Cruz for the GOP nomination say they would vote for Trump in November, while 13% would vote for Clinton and 10% would not vote. Among Republicans who back John Kasich, just 50% would vote for Trump and 19% would vote for Clinton, with 22% saying they would sit out the general election.

General election polling this early should be viewed with skepticism, but if there’s anything at all to this, it’s trouble — nontrivial numbers of Republican voters either might vote for Clinton or stay home. And again, even Republicans are worried about this scenario impacting GOP control of the Senate.

This could also end up happening even if Trump is not the nominee. If Republicans do manage to nominate someone else at a contested convention, Trump could try to run as a third party candidate in at least some states (logistics permitting) or, if not, he could call on his supporters to oppose the GOP establishment candidate, potentially depressing GOP turnout this way or otherwise producing untold ruptures among Republicans.

I have seen it reported (I cannot find the link) that some GOP leaders are hoping that, if they refuse to consider Garland, and if it’s looking likely that Republicans will lose the White House with Trump as the nominee, the specter of a President Hillary picking the next Supreme Court justice could drive up Republican turnout, as GOP voters seek to keep the Senate in GOP hands to defeat her nominee. If this is so, then some Republicans are hoping that refusing to act on Garland not only keeps the base engaged, but also gives Republicans an active reason to vote for GOP Senators, even as other Republicans worry that Trump — in one way or another — could have the opposite effect. It’s a mess.

My point isn’t to predict that Republicans will lose the Senate. Rather, it’s that, if they are hoping that not budging on Garland will help them hold it, Donald Trump is potentially a ticking time bomb at the center of that whole plan.