Paul Ryan has continued to stand behind Donald Trump this summer despite the many, many, many things Trump has done and said that would make a more principled politician reconsider his support. Ryan has justified it all by arguing repeatedly that he and his fellow Republicans could accomplish far more with Trump in office than with his opponent. It turns out, however, that Trump does not feel the same way about the House speaker.

In an interview with the Washington Post on Tuesday, Trump refused to endorse Ryan in his upcoming GOP primary election in Wisconsin against Tea Party–style businessman Paul Nehlen. “I like Paul [Ryan], but these are horrible times for our country,” Trump said of the highest-ranking Republican in the U.S. government. “We need very strong leadership. We need very, very strong leadership. And I’m just not quite there yet. I’m not quite there yet.”

The end of this statement seemed like a biting reference to a statement about Ryan’s own ability to support Trump that the speaker made in May, when he said “I’m not there right now” (Ryan eventually came around to endorsing the Republican nominee). The political science term for all of this is: OMFG.

At this point, nothing Trump does should surprise anyone, but this is a stunning decision. It comes just two weeks after Ryan tried to rally his party at the GOP convention and Trump officially became the Republican Party nominee. It also comes at a time when we are starting to see small but significant cracks in the façade of GOP unity following Trump’s ill-conceived feud with the gold star parents of a fallen Muslim American soldier.

According to the Post, Trump went after other high-profile Republicans who have expressed their support for him. The GOP nominee said he is not supporting Arizona Sen. John McCain in his primary in Arizona, while also singling out New Hampshire Sen. Kelly Ayotte, in the paper’s words, “as a weak and disloyal leader” in her home state. (McCain offered one of the more severe rebukes of Trump’s comments about the Khan family but did not rescind his support; Ayotte has said she’ll vote for Trump but says she’s not formally endorsing him.) For Republicans who have been trying to walk a fine line by supporting Trump but still renouncing his most vile comments, then, Trump has now sent a clear message: Your support does not guarantee mine.

Making this move all the more remarkable is that there is clearly a method to this madness. This may not be a brilliant way to become the president, but it is a brilliant way to humiliate your enemies. If Ryan (or McCain) were to finally rescind his presidential endorsement over this—after standing behind Trump during everything that came before it, including comments Ryan conceded were a “textbook” case of racism—the decision will look petty, not principled. Trump has no doubt thought of that. He doesn’t often appear to be a man choosing his words carefully, but his “I’m not quite there yet” construction clearly echoes Ryan’s comments earlier this year and means he thought about these words. Somewhere right now, Ted Cruz is smiling.

Read more Slate coverage of the 2016 campaign.