Spoiler: He will not, in fact, tank the tax reform bill. Rubio is not so bold that he’d blow up the GOP’s best chance at passing major legislation because it didn’t do enough to help lower-class families. Rubio is … not so bold, period. He was bold in 2013 when he tried to play salesman to the right for the Gang of Eight bill, thinking that if he pulled it off it might catapult him to the presidency three years later. He learned a hard lesson.

But he’s right on the politics here. And if Trump cared less about winning for the sake of winning and more about helping the blue-collar populists who got him elected, he’d join Rubio in pounding the table. You want a “workers’ party”? Shave a tiny bit off the corporate tax cuts and add it to the child tax credit. As it is, in the unlikely event that Rubio really digs in on this, Trump’s less likely to side with him than to start tweeting about “Little Marco” again.

“I’ve been pretty consistent in my communications on this issue and that is I want us to see the refundable portion of the child tax credit increased from its current number,” Rubio told reporters on Capitol Hill on Thursday. “If it stays at $1,100, I’m a ‘no.’ Let’s hope it doesn’t.”… Rubio — along with Sen. Mike Lee of Utah — has been working for months to make the child tax credit more refundable, something the senators argue will help lower-income Americans, but so far their efforts haven’t convinced leaders who are trying to craft a tax bill that still meets Senate rules and doesn’t cost more than $1.5 trillion… “Sen. Lee is undecided on the bill in its current forms,” spokesman Conn Carroll told CNN in a statement. “Sen. Lee continues to work to make the CTC as beneficial as possible to American working families.”

A nonrefundable credit is one that’s applied against your total tax liability, but not a dollar more. If you owe the feds $1,000 and you’re eligible for a credit of $1,001, you don’t get that extra dollar back. With a refundable credit of the sort Rubio and Lee want, you do. A low-income family that owes little to nothing in income tax would actually get a “refund” from Uncle Sam in the amount of the credit. It’s redistribution, but I’ll remind you again that a crop of more or less dogmatic fiscal conservatives ran against a highly undogmatic moderate in the 2016 GOP primaries and were roundly beaten. Rubio and Lee are willing to sacrifice a little of their fiscal dogma in the name of making life a bit easier for families, specifically low-income families. Ideally those families will use a larger child tax credit to pay for extra diapers, clothes, child care, and so on rather than 75-inch flat-screens, and some lower-income couples who fear the expense of having kids will feel more comfortable starting a family, increasing the birthrate and adding to the next generation’s tax base. Ideally.

Right now the CTC stands at a meager $1,000. Rubio and Lee want to not only expand it, they want to make it refundable against federal income tax and federal payroll tax. Even the poor have to pay that one; Rubio/Lee would put some of that money back in their pockets to help pay for their kids. According to Lee, Republicans have already agreed to make some portion of the CTC refundable against the payroll tax although the specific amount is as yet undetermined. As for expanding the credit, he and Rubio wanted it doubled to $2,000 in the Senate version of the tax bill and offset by a tiny reduction in cuts to the corporate tax rate, but their amendment went down in flames. The corporate rate must drop to 20 percent and not a smidgen less, they were told by leadership. It’s essential to economic growth!

Then they went to conference with the House, cut the top rate for the wealthy from 39.6 percent to 37 percent, and kicked the corporate rate up to 21 percent to pay for that. They won’t take a larger cut from corporate America to help lower-class Americans with kids, but to help the donor class? Sure, no problem. That’s also being done in the name of growth, supposedly. See why Rubio’s annoyed enough to issue empty threats about tanking the bill?

But wait, you say. He can’t tank the bill. He’s only one vote and the GOP has 52 right now; Doug Jones won’t replace Luther Strange in the Senate for a few weeks at least. Even if Rubio *and* Mike Lee balk, McConnell’s still got 50 and a tiebreaker in Mike Pence — in theory. Remember, though, that Bob Corker voted no on the original Senate tax bill two weeks ago and isn’t crazy about the version that’s coming out of conference. And he’s retiring next year, which means he’s under no pressure to help Trump out by holding his nose and voting yes. Even if McConnell can convince Lee to vote yes and he loses only Rubio and Corker, he still has a huge problem. Thad Cochran is ailing and frequently away from the Senate and McCain is being treated for side effects of cancer at the moment. If they’re both too ill to attend the floor vote on the final bill, Rubio (and every other Republican) will in fact be the 50th vote. Any one of them could tank it.

But he won’t tank it, even though he’s very well positioned politically to have this fight. He was just reelected and doesn’t have to face voters again until 2022; he was sufficiently disillusioned with politics last year that he was planning to retire and go make money, which he could still do five years from now; his idea of taking a tiny bit more money from corporations and handing it to families basically sells itself; and if Trump gives him a hard time for his opposition, he can accuse the president credibly of selling out the same populist voters who swept the GOP to victory last fall, a dangerous charge for Trump to defend himself from. He *should* take a stand, but he won’t. It’s just not who he is. He’ll get some token concession on the CTC to let him save face, i.e. a $1,400 credit instead of $1,100, and then he’ll vote yes. No one doubts it, do they?