To be clear, I’m not encouraging him to do so. Sanford may be the last true fiscal conservative left in the House. But various political news outlets have spent the last few days marveling that Sanford really could lose his primary. He’s a former governor, so his name recognition is sky high. He’s never lost an election. He holds a safe seat in crimson red South Carolina. He should be money in the bank.

But one thing distinguishes Sanford from virtually every other House Republican standing for reelection. No, not his fiscal record. Not his famous scandal either. It’s the fact that he’s a harsh Trump critic, not quite as frequent or adamant as Jeff Flake but probably the closest thing to him in the House among non-retiring incumbents. The locals back home have noticed too. There’s no obvious explanation for this recent poll except that Trumpers in his district are itching to punish Sanford:

A new poll shows Republican Katie Arrington is within striking distance of defeating incumbent U.S. Rep. Mark Sanford, a candidate who has never lost an election in his political career…

Less than one point separated Arrington and Sanford, with 39 percent saying they would pick Arrington while 39.7 percent said they would choose Sanford…

But there is opportunity for both candidates as the primary nears: 21.3 percent of likely Republican primary voters polled were still undecided.

A lead of less than a point is a disaster in the making against a no-name like Arrington, made all the more shocking by the fact that the famously stingy Sanford has coughed up a few hundred grand in ad spending on the race. He’s fighting for his political life here and there’s every reason to believe that he’s losing. And his opponent is running shrewd ads of her own, as you’ll see below. You don’t need to worship the president, she’s been telling interviewers, you just need to not go out of your way to offend him, as Sanford seems to have done. How can you expect to advance your legislative priorities when you’ve chosen to make an enemy of the White House?

And he has made an enemy of them. Politico recalls some of his greatest anti-Trump hits:

Sanford, long known for wearing his emotions openly and speaking his mind, has been one of the most high-profile Republican Trump critics in Congress. He’s called the president’s tariffs on steel and aluminum “an experiment with stupidity.” He’s called Trump’s disparaging remarks about Haiti and African nations “something stupid.” He’s said that Trump has done some “weird stuff” in office.

During the 2016 campaign, Sanford said Trump should “just shut up” and stop focusing so much on his critics. He’s said that the president was “partially” to blame for the toxic rhetoric that led to the shooting of House Majority Whip Steve Scalise (R-La.). He’s said that “trading slights seems essential” to Trump’s personality, and he gave an extensive interview to POLITICO Magazine in which he said the president had “fanned the flames of intolerance.”

The primary’s tomorrow. In all likelihood, all it would take to send Sanford down to defeat by tilting undecideds against him is a tweet from Trump endorsing Arrington. But that tweet will probably never come. The president’s a little occupied in Singapore right now and has more important things on his mind than House primaries. The mystery is why he didn’t endorse Arrington sooner, when he had time and every opportunity to do so. The usual answer to that question, certainly in Senate races, is that it’s dangerous to back newbies against incumbents since it puts you at risk of a reprise of the Roy Moore disaster. Stick with the guys who are already in office, whom we know can get elected. They’re well known, there’ll be no surprises in the general election, and they’ll rubber-stamp your agenda once they’re back in Congress (even Sanford usually votes with Trump).

But that logic doesn’t work here. Even a no-name Republican as nominee will hold the seat. And Trump has been a good soldier for the party lately, partnering with McConnell to discourage populist insurgencies against Senate incumbents. Surely McConnell and Ryan would have indulged him *one* endorsement off the beaten path in the primaries in the name of taking out a Republican who’s been a thorn in his side. Why didn’t POTUS do it? I genuinely don’t understand. It’s surprising.

Here are Arrington’s ads. Of note, via BuzzFeed, is that she’s not just attacking Sanford for his scandal and for alienating Trump. She’s also swiping at him for opposing so much legislation, which seems like a dig mainly at his dogged fiscal conservatism, “Saying ‘no’ doesn’t solve a problem,” she told BuzzFeed. “And Mark is the king, he is the master of saying ‘no.'” Five years ago that would have been music to populists’ ears. Now, with the feds still spending mountains of cash but under a Republican president, it’s an indictment. We’ll find out in 24 hours how much of one.