Twitter back-and-forth caught my eye:
Philip Klein: Imagine how differently the Hagel vote would have turned out had Dewhurst won TX Sen primary.If the honest answer is probably "we don't know," it's still worth a bit of speculation.
Dan Drezner: Not an iota's worth.
Philip Klein: Disagree. Cruz was the leader of the opposition publicly & privately & his presence is has moved Cornyn to the right.
Dan Drezner: Cruz has alienated as many as he impressed. And in yesterday's vote, wavering GOP senators followed McCain's lead, not Cruz.
Would Republicans in general decided to target Hagel if Cruz wasn't a public and private leader of the opposition? It seems fairly likely to me that they would have. Republicans really love the theme of accusing people of abandoning Israel. It works for them on many levels. Not just the almost certainly futile effort to win Jewish votes, and not just currying favor with pro-Israel Christians. It's also a rare area of foreign policy in which they can advance a plausibly popular position that doesn't actually involve advocating war or the threat of war. Without, that is, alienating the party's hawks. In other words, considering both unity within the party and popularity outside of it, ultrafanatical support of Israel may be the best possible issue within foreign policy and national security for the GOP. The only real drawback is that it doesn't actually involve differences with anyone, but that's made up by exaggerating or inventing any deviation from standard American political support for Israel. Thus, the enthusiasm of the GOP in opposing Hagel.
What Drezner says about wavering Senators following McCain's lead is probably correct, although that doesn't answer the question of why McCain supported cloture. Suppose that without Cruz we still get basically the same anti-Hagel sentiment among Republicans, perhaps with someone else grandstanding (and, as Drezner hints, perhaps in a less irresponsible way). Would McCain still have stuck with the opponents through the first cloture vote? Possibly! On the other hand -- maybe better leadership for Hagel opponents would have put McCain solidly on board with the filibuster, thus putting Hagel in far more trouble than he currently appears to be (McCain and several other Republicans who voted against cloture yesterday have said that they plan to flip and vote for cloture after the Senate recess next week).
What we do know is that he's certainly impressed parts of the GOP-aligned press -- and that he's annoyed enough Senators to have generated, say, an item by Elspeth Reeve today reporting on public and private GOP rebukes to Cruz. Careful, however: those kinds of stories are almost always meaningful, but can be tricky to interpret (that is, some Senators are almost certainly annoyed by Cruz's behavior, but that doesn't necessarily mean he isn't influencing them).
My best guess would be that Cruz himself didn't make a lot of difference on Hagel. The idea that there was a norm against cabinet filibusters followed by Republicans the last few years, in my view, doesn't hold up at all. All that's happened is that for a variety of reasons we haven't had a nomination come to the floor with solid GOP opposition, so it hasn't really been put to the test. But I'll fully admit that's a best guess, not fact.