Trump critics were breathing heavily this morning after he retweeted a GIF of him driving a golf ball off of Hillary Clinton’s back but the item below remains the most surprising thing to appear on his Twitter account in the past 24 hours. I thought he had all but abandoned Luther Strange after endorsing him a few weeks ago in the Alabama Senate primary, which would have made sense. Strange has trailed Roy Moore badly in independent polls and is being championed by Mitch McConnell, currently one of POTUS’s least favorite Republicans. Trump’s populist base, led by Steve Bannon, is also all-in on behalf of Moore.

The safe play, especially after pissing off some of his fans this week by dealing with Democrats on immigration, would have been for Trump to limit any further endorsements of Strange before the runoff to Twitter or even to decline to say another word about the race, hanging him out to dry. Doubling down on him is a lose/lose proposition. If Strange wins now, Trump’s base will be angry that he rescued the establishment candidate from near-certain defeat, and if Strange loses, the media will ooh and ahh that Trump’s endorsement doesn’t mean much even in deep red Alabama. POTUS couldn’t save the incumbent, they’ll say. Maybe he really is losing his fans.

But no, against all odds, he’s going all-in. And just a day after populist Mo Brooks endorsed Moore, too:

https://twitter.com/realDonaldTrump/status/909191177810915328

What’s he thinking? The lazy psychological read is that Trump’s ego intervened when he saw that Bannon was on the verge of beating “his” guy and now he’s going to show the Breitbart crew that populist America still follows him, not Bannon. More likely, though, is that POTUS was muscled into doing a rally for Strange, however reluctantly, by Republican donors loyal to McConnell. If he abandoned Strange, that might have touched off a wave of populist challenges to GOP incumbents next year. (Which is exactly why Bannon is so keen to see Moore win, of course.) And if that had happened, with Trump sitting by and doing nothing about it, a lot of thick wallets might have snapped shut.

Deep-pocketed supporters of Senate Majority Leader Mitch McConnell (Ky.) and other GOP leaders have resolved to fight a protracted battle over the next year for the soul of the party in congressional primaries. “It’s shaping up to be McConnell, the Senate Leadership Fund and the Chamber against Bannon,” said Scott Reed, the senior political strategist for the U.S. Chamber of Commerce. “And we will take that fight.”…

Allies of McConnell have been blanketing the Alabama airwaves to shrink Moore’s polling lead. After spending nearly $4 million on ads before the first primary vote in August, the Senate Leadership Fund plans to blitz the state with another $4 million before the Sept. 26 runoff. So far this year, the super PAC has raised more than $11 million, including a $1 million infusion from hedge fund manager Paul Singer last month, federal filings show.

The Chamber of Commerce is planning to kick in for mailers and GOTV operations on Strange’s behalf, knowing that the more populists there are in the U.S. Senate, the more protectionist U.S. economic policy is going to get. Trump would like that just fine, I’m sure, but he won’t like watching the Republican business class walk away from bankrolling his 2020 effort as punishment.

There are other reasons why he’s willing to gamble on Strange:

Tennessee Sen. Bob Corker, who is up for reelection in 2018 and faces the prospect of a primary challenge, spoke extensively with Trump on Friday. According to two people familiar with the conversation, Corker told Trump that Strange’s fate hinged on the president going to bat for him…

Behind the scenes, the president has expressed a fondness for [Strange]. During the push to repeal Obamacare this year, Trump has remarked, the senator gave his support without asking for any favors in return. At a time when some Senate Republicans were uneasy about getting behind the bill, the president was impressed.

For any other Republican president, the right move here would be obvious. You back your party’s incumbents because they’re more likely to beat the Democrat in the general election than a no-name populist who pulls an upset in the GOP primary is. (See, e.g., Mike Castle and Christine O’Donnell.) A strong presidential endorsement of the incumbent will discourage most of those populists from trying in the first place, in fact, which means the GOP gets to save big bucks by not having to spend money on contentious primaries. In the end, most incumbents will vote with the White House 80-90 percent of the time despite their establishment leanings; that’s a better bargain than losing the seat to a Democrat who’ll vote with Trump 20 percent of the time.

Trump’s not the average Republican president, though. If he’s serious about shifting to the left, as his DREAM deal with Schumer and Pelosi hints, he’s better off with a Democrat in the seat in some key ways than with a Republican incumbent. Democrats are more comfortable with the nationalist parts of his agenda, like protectionism and infrastructure spending, than the GOP leadership is. And the stakes in Alabama couldn’t be lower: The state is so red that Roy Moore almost certainly will win the general election if he wins the primary, particularly given how famous he is there for his Ten Commandments and gay marriage battles on the state supreme court. If Trump had switched his endorsement to Moore and McConnell’s nightmare scenario came true, with populist challengers suddenly jumping into GOP primaries across the country, what’s the worst that could happen *from Trump’s perspective*? Next year he gets a Senate with a few more Democrats and a few more populist Republicans, both of which weaken McConnell’s hold on the caucus and push the party towards the center? That … sounds like not a bad deal for a centrist president who already thinks McConnell’s a weak leader who’s retarding his agenda.

There are reasons for him to stick with Strange, though, besides the fundraising issue I mentioned above. Everyone understands that he has it in for Jeff Flake and is trying to engineer a primary challenge to him in Arizona. Senate Republicans hate that but Flake is unpopular and Trump’s annoyance is understandable insofar as Flake has been one of his most vocal critics on the right. McConnell and his caucus don’t want to see the White House trying to take out one of its own but they may have no choice but to let that slide, given how intent Trump seems to be on it. It’s personal more so than it is political. If Trump tried to take out Strange, though, by switching to Moore, that would be political, not personal. It would be Trump effectively declaring war on his own caucus, at which point any semblance of cordiality between them might break down. We can blather all day about Trump’s centrist potential in working with Democrats; the fact remains that if McConnell stops pushing his agenda and Senate GOPers start finding excuses not to vote for Trump initiatives, he’ll never be able to replace those lost votes with enough Democrats to get his program through. He simply can’t afford to piss off a co-equal branch controlled by his party too much. And abandoning Strange under pressure from Bannon would have pissed them off a lot.

So, in all likelihood, he’s going to wing it by supporting or opposing Republican incumbents not based on whether they’re “establishment” or “populist” but whether they’re pro- or anti-Trump, which is perfectly in keeping with his worldview. If you’re a pro-Trump incumbent like Strange: Endorsed. If you’re an anti-Trump incumbent like Flake: Bye. Exit question: Where does that leave Dean Heller?