One thing to remember about the Senate Budget Committee is that, as presently constituted, it has twelve Republicans and eleven Democrats. What this means is that every Republican on the committee can sink a Budget Committee bill by joining with the Democrats. The assumption here, of course, is that none of the Democrats on the committee will be willing to vote for this hypothetical bill. But I think it’s safe to say that there aren’t any Democrats serving on the Budget Committee who would vote for a partisan tax bill that disproportionately rewards the rich, raises taxes on many in the middle class, and explodes the deficit. Therefore, in order to advance that kind of tax bill to the floor, the Republicans have to stay united.

Senator Bob Corker of Tennessee is one of the twelve Republican members of the Budget Committee. And he’s been increasingly clear in his threats that he isn’t interested in the tax plan the White House and his Senate colleagues are cooking up. He appeared on Meet the Press a week ago and said that the deficit is “the greatest threat to our nation.” And he continues to talk about this:

“I felt there was a period, two or three years ago, when there was a real seriousness about trying to solve our fiscal issues,” said Sen. Bob Corker (R-Tenn.), a longtime deficit hawk who is part of a scarce group of Republicans consistently preaching restraint. “When the election result turned out what it was [in November], any thought of fiscal responsibility has gone out the window.”

He added, “It’s very disheartening to me that when the other side of the aisle was in charge we cared about fiscal issues, and now that we’re in charge we don’t care about fiscal issues. It’s very disheartening.”

Speaking of White House Office of Management and Budget (OMB) Director Mick Mulvaney, Corker is just barely diplomatic:

Mulvaney’s more pragmatic approach marks a major evolution. Six years earlier, during a fight over whether to raise the debt ceiling, Mulvaney picked up a Bible and read a verse from Proverbs 22 to colleagues: “The rich ruleth over the poor, and the borrower is servant to the lender.”

Corker said Mulvaney’s transformation from a budget warrior to allowing larger deficits is emblematic of others in the party.

“My gosh, this was a guy that had very much of the same feelings that I had about these issues, and obviously he’s ended up being in a different place,” Corker said.

Corker is unusual in that he’s a Republican who believes in intellectual consistency and is willing to practice what he preaches. He’s already cast a vote against the annual defense bill because it “exceeded congressionally mandated spending caps by more than $80 billion,” and he didn’t support the Hurricane Harvey disaster relief bill because it also extended the debt ceiling and didn’t include any offsets.

Now, in truth, the Budget Committee isn’t responsible for formulating the final tax bill. The Finance Committee, led by Sen. Orrin Hatch of Utah, will have the lead role on that. The Budget Committee just needs to get the process rolling by moving a budget that will include reconciliation instructions allowing the Republicans to pass the Finance bill with a mere fifty votes instead of the sixty votes typically needed to overcome a filibuster.  A couple of weeks ago, Corker supposedly struck a deal with another member of the Budget Committee, Senator Pat Toomey of Pennsylvania, that will actually allow the Senate to pass a more expensive bill than the House.

Speaking of the House, they actually passed their budget resolution bill last week, but barely. It takes 218 votes to get a majority in the House, and the resolution only got 219 votes.

I anticipate that Corker will stick by the deal he made with Toomey and not hold up the budget bill in committee. But there are two things to keep in mind about that. The first is that he recently announced that he will not seek reelection, so he’s free to do pretty much whatever he wants. He’s clearly not happy with the direction the Senate is headed on the tax bill, so it’s probably best not to antagonize him. Secondly, even if he doesn’t stand in the way of allowing the process to begin, the Republicans will probably need his vote at the end in order to pass the resulting legislation. If Corker doesn’t support the final bill, the Republicans can only afford to lose one other senator or their effort to get around the filibuster will fail.

On that score, please remember that Sen. John McCain voted against similar tax cuts when President George W. Bush proposed them. Considering his precarious health, he may or may not be available to vote. But it’s not certain at all that he’ll support Trump’s tax bill and he’s already demonstrated that he’s willing to blow up a process he doesn’t like with his vote against the health care repeal bill.

As of now Rand Paul also appears to be a ‘no’ on the tax bill, and I’m not sure Sen. Susan Collins will be ready to vote for it, either. In other words, the Republicans really need to keep Corker happy and on board. Even with his vote, the effort might fail.

Which makes it very curious that the president decided to go to war with Corker today on Twitter. Now, Trump is probably thinking about different subjects. As the chairman of the Foreign Relations Committee, Sen. Corker has a lot of influence over our policy toward Iran. Corker has also been critical of the president’s judgment and temperament in recent months, especially after Trump’s disgusting reaction to the tragedy in Charlottesville, Virginia. In reaction to Trump’s diatribe against him, Corker has now come out twice with harsh language against the president. First he said that “the White House has become an adult day care center. Someone obviously missed their shift this morning.” And then he criticized the president’s remarks about North Korea and accused Trump of treating his office like “a reality show” and putting the world “on the path to World War III.”

In a telephone interview with the New York Times, he went even further:

“He concerns me,” Mr. Corker added. “He would have to concern anyone who cares about our nation.”

The senator views Mr. Trump as given to irresponsible outbursts — a political novice who has failed to make the transition from show business.

Mr. Trump poses such an acute risk, the senator said, that a coterie of senior administration officials must protect him from his own instincts. “I know for a fact that every single day at the White House, it’s a situation of trying to contain him,” Mr. Corker said in a telephone interview.

He clearly is more interested in sounding the alarm about the president than in strengthening him by pushing forward his agenda.

The senator, who is close to [Secretary of State Rex] Tillerson, invoked comments that the president made on Twitter last weekend in which he appeared to undercut Mr. Tillerson’s negotiations with North Korea.

“A lot of people think that there is some kind of ‘good cop, bad cop’ act underway, but that’s just not true,” Mr. Corker said.

Without offering specifics, he said Mr. Trump had repeatedly undermined diplomacy with his Twitter fingers. “I know he has hurt, in several instances, he’s hurt us as it relates to negotiations that were underway by tweeting things out,” Mr. Corker said.

“Look, except for a few people, the vast majority of our caucus understands what we’re dealing with here,” he said, adding that “of course they understand the volatility that we’re dealing with and the tremendous amount of work that it takes by people around him to keep him in the middle of the road.”

It should also be remembered that Corker was a pretty strong supporter of Trump during the campaign and served on his foreign policy advisory committee. He wasn’t among those who abandoned Trump after the Access Hollywood sexual assault tape came out. That he’s clearly saying that Trump is a dangerous lunatic who might get all of humanity killed is highly significant and not just some sour grapes from someone who never thought Trump should be entrusted with our foreign policy in the first place.

He’s now likely to see the battle over tax reform as more than a debate on the merits. He’s likely to see it in terms of whether it gives Trump a boost and some staying power. He clearly doesn’t like the tax proposals as they stand, so his primary reason for going along with the plan would be to help his fellow Republicans avoid another high-profile legislative failure that might imperil their congressional majorities. He now has to weigh his loyalty to the party and his colleagues against what he considers to be bad policy and a truly reckless and dangerous president. He could easily conclude that his highest priority is not the short-term fortunes of the Republican Party but the safety of humanity. And based on that, helping Trump accomplish something he doesn’t agree with is probably low on his priority list.

The experience of being personally attacked by the president probably introduces additional considerations, including simple pride. No one wants to look they’re caving to that kind of pressure.

On the whole, it’s hard to see what the president is trying to accomplish with his attacks on Senator Corker. He clearly doesn’t understand how much power Corker has to thwart his ambitions. And the spectacle strongly supports Corker’s basic contention that Trump is not fit for the office he holds and doesn’t have a grasp of how to do the job.