Or is it?
Republican Senators could block any US Supreme Court appointment not to their liking, not only from lame duck President Obama but from a possible President Hillary. That’s the kind of thing the Democrats, knowing the Republicans would deal eventually, have done.
What if the Republican-controlled Senate held out indefinitely? Five-to-four decisions favoring the Democrats would become impossible. But so would five-to-four decisions favoring the Republicans. Unless something changed there might be deadlock on partisan issues, which probably wouldn’t be a bad thing. But eventually things would change. President Hillary could appoint someone more moderate. The Republicans could lose control of the Senate. Additional justices could die or retire.
OTOH, a demonstration of firmness, even irrational firmness, by Congressional Republicans might pay dividends in the long run. Reagan gained considerable, perhaps decisive, advantage in foreign affairs by firing the striking air controllers.
OTOH, Reagan was an individual and the Republican Senatorial delegation is a coalition. It’s relatively easy to weaken a coalition by bribing or pressuring marginal members to drop out. The prevailing incentives do not favor Republican institutional backbone.
Interesting times ahead.