Barack Obama's choice for the Supreme Court is a twice over. Merrick Garland, a D.C. Circuit Court appellate judge, is a moderate, and he's 63 years old.

Republicans will regard him as a radical liberal and publicize quotes from his judicial career "proving" he is out of the mainstream. Keep in mind, however, that Republicans also consider Chief Justice John Roberts a liberal traitor.

Garland is a less long-term replacement for the late Antonin Scalia than some other possibilities, such as the 49-year-old Sri Srinivasan. Obama could have chosen an even older nominee as an even more obvious compromise, but went straight up the middle.

Unlike Obama, Senate Majority Leader Mitch McConnell and Judiciary Chairman Chuck Grassley are in no mood to compromise. While senators have a right to block a candidate they think is out of the mainstream, will their blockade against any Obama nominee hold now that he has chosen someone to be confirmed, rather than a nominee to help Hillary Clinton get elected in November?

Republicans could face a Clinton victory in November and a Democratic majority in the next Senate, giving the new president a chance to pick a younger and more liberal justice. They also think Donald Trump, the front-runner to be the Republican nominee, would be entirely unreliable when it came to Supreme Court nominations (or anything else).

But Senate Republicans could be less worried about that than they are about their own electoral consequences in 2016.

What do they fear most: the possibility of losing the moderate swing vote in the presidential contest in November or the chance that a more die-hard conservative will challenge them in their own Republican primaries?

Moderate Republican Sen. Mark Kirk of Illinois won his primary on Tuesday night. He can focus now on the general election. But for most of his GOP colleagues who are running for re-election, the primary is still to come, and in some states the filing deadline hasn't been reached yet. Even without the threat of a primary battle, Republican senators may still worry more about losing the enthusiastic support of conservative activists than they do about the possibility that swing voters will care about whether a Supreme Court nominee gets a fair hearing and a vote in the Senate.

The job for liberal activists, as Rick Hasen wrote at TPM, is to change that calculation: to show Republican politicians that there's a price to pay for obstruction. If they succeed, Garland could have a chance to be confirmed. If these efforts fail, it will just be another example of partisan polarization.