Via the Free Beacon, here’s the big Cruz/Rubio dust-up from last night. Cruz has been waiting a long time for Rubio to be pinned down by a question on immigration at a debate and Rubio’s been waiting a long time for the chance to pin Cruz down on his own view. Cruz wins this exchange because he got to link Rubio to Chuck Schumer and amnesty, which, believe it or not, will come as news to some sizable chunk of low-information Republican voters.

Rubio’s crafty, though. Watch how he puts Cruz on the defensive at 5:30 by demanding a straight answer to the lingering mystery of what President Cruz would do with the millions of illegals who remain in the U.S. after new security measures are imposed. For, oh, around two years now, Cruz has steadily ducked that question. Lately, as reporters and rival candidates have zeroed in on it, he’s had to give a slightly more specific non-answer: He will not, under any circumstances, clearly say that he’s open to legalizing illegals — gotta keep those Trump fans happy — but he also will not, under any circumstances, clearly say that he’s ruled it out. (Although, interestingly, his campaign chairman will.) All he’ll say is that we’ll have a “conversation” about legalization after we tighten enforcement first and see some illegals self-deporting. This sort of hedging drives Team Rubio nuts, as their guy’s been sweating over amnesty since 2013 while somehow Cruz, the great RINO scourge, has managed to avoid taking a firm position himself. So Rubio insisted on it last night when the opportunity finally arose. Cruz’s response: “I do not intend to support legalization.” You don’t intend? If Mitt Romney had said circa 2011, “I do not intend to keep ObamaCare in place as president,” the tea party would have metaphorically grabbed him by the throat. Most viewers missed the significance of Cruz’s caveat, I’ll bet, because they’re not following this issue closely, but if you wanted further evidence that Cruz isn’t going to pursue a Trumpian “everybody out” policy as president, now you’ve got it.

If you’re hazy on the background here and aren’t sure whom to believe when Rubio claims Cruz has supported legalization in the past and Cruz denies it, read this. Rubio’s talking about Cruz’s proposed amendment to the Gang of Eight bill two years ago that would have increased work permits for illegals while also stripping the path to citizenship out of Rubio’s bill. Cruz says he offered that amendment simply as a poison pill: He wanted to show that Democrats only cared about citizenship for illegals and would reject an amendment that denied that to them even if it also allowed them to stay and work. The amendment was indeed rejected. I think Cruz is being too cute by half, though. Right now, in a Republican primary, he’s claiming the amendment was a poison pill to appease border hawks. Don’t take the work-permit thing at face value! It was all just a ploy to expose the true Democratic agenda. Next year, though, if and when he’s the nominee and needs to deflect Hillary’s attack that he’s “anti-Latino” or whatever, he’ll point to his amendment as evidence that he really is open to legalization. By then, Republicans will be all in on beating Clinton and will forgive him the flip-flop in the name of pandering to the center. In fact, for a guy who was supposedly pushing a poison pill at the time, Cruz seemed pretty willing in 2013 to give reporters the impression that he was comfortable with legalizing illegals:

This @TexasTribune article highlights Cruz's strategic ambiguity in immigration: https://t.co/pFTphSrZbG pic.twitter.com/wsRlzK1oCW

— Liam Donovan (@LPDonovan) December 16, 2015

Note the last sentence there. Like I say, though, most people watching last night wouldn’t pick up on this. Most of them are going to come away remembering little more than that Rubio was on the defensive and that Cruz, who opposed the big amnesty bill, said something about how he wouldn’t legalize illegals as president. Advantage: Cruz. I think Mike Warren is on the mark with this assessment of who had the better debate:

But Cruz is on or near the top in Iowa, coming into his own as a candidate and picking up momentum. The Texas senator is increasingly looking like a reasonable conservative alternative to the Trumpmania within the party. Rubio, meanwhile, has been sitting in the middle of the top of the pack in Iowa, New Hampshire, and nationally for weeks. Rubio didn’t need simply to mitigate the damage from finally facing difficult questions about his chief weakness. He needed to knock Cruz off his game, too. But ever the nimble debater, Cruz showed he was prepared to deny Rubio’s claims and reassert his commitment to principle. The confusion over Cruz’s position may end up looking more like a desperate Rubio trying to take down a surging rival.

Right, and not only is Rubio’s base smaller than Trump’s or Cruz’s (right now), I think it’s also less solid. If you like Trump, only Trump (and maybe Cruz) will do. If you like Cruz, you see him as the only true conservative choice. If you like Rubio, well, you might like him for various reasons. He has his devoted fans, but some people prefer him because they think he’s the most electable Republican, some like him because they want a “reasonable” nominee and hate Trump and Cruz, some see him as an important generational change, and so on. In theory, that’s an argument for why Rubio is the likeliest nominee: He can consolidate the center with the right and bring in undecideds on “electability” grounds. In practice, though, I think it leaves him more vulnerable to having votes poached than Trump or Cruz are. If you want a “reasonable” centrist Republican who’ll take it to Trump and Cruz, why not the two-term governor Christie? That is to say, for some (but of course not all) Rubio fans, he’s a placeholder right now as the candidate who can block the GOP’s less electable potential nominees from the nomination. And placeholders can be replaced. The more radioactive he becomes to some Republicans over immigration, the less likely it’ll seem that he really can stop Cruz (or Trump) if it comes to that.