Politically, it’s not entirely clear who has the upper hand in this fight. Immigration reform seems like a more toxic issue for conservatives than the N.S.A.’s metadata program, which has long had strong critics in the libertarian wing of the Party—although, obviously, national-security issues are now dominating the public debate. And Cruz seems slightly more comfortable defending his N.S.A.-reform vote than Rubio does defending his immigration-reform vote; on Saturday, Cruz also said that Rubio was afraid of “the criticism that he has received that he is not willing to protect the Fourth Amendment privacy rights of law-abiding citizens.” But while the politics are unclear, the implications for governance are more obvious.

Numerous governors have already dropped out of the race, candidates who, despite their flaws, ran large states and were reëlected by voters: Scott Walker, of Wisconsin; Bobby Jindal, of Louisiana; Rick Perry, of Texas. The governors still in the race—Jeb Bush, the former governor of Florida; Mike Huckabee, the former governor of Arkansas; John Kasich, the governor of Ohio; and Chris Christie, the governor of New Jersey—are struggling.

It now appears that we are entering a period of the campaign in which the two Republican senators who may have the best shot at unseating the front-runner, Donald Trump, and winning their party’s nomination are veering into a potential murder-suicide pact over who was more complicit in actually trying to get something accomplished in Washington. The lesson for any senator who aspires to higher office is clear, and depressing: it’s safer to do nothing at all than it is to try to solve a big problem.