Senator Bob Corker said Thursday he doesn’t think President Donald Trump has demonstrated “stability,” “competence,” or understanding of “the character of this nation.”

Normally, that would be a stunningly personal attack for a senator of one party to launch against a president of the other party. But Corker and Trump are both — at least in name — Republicans.

Aside from the most prominent issue at hand — Trump’s reluctance to unequivocally denounce white supremacists in the wake of lethal violence in Charlottesville, Virginia, last week — there’s a lot of bad blood between Trump and his putative Republican allies in the Senate because of his attacks on Majority Leader Mitch McConnell, embattled incumbent Sen. Jeff Flake, R-Ariz., and others.

It shouldn’t make much difference to Trump if he has to fend off a few verbal arrows from senators who want to position themselves against him. After all, Corker’s the chairman of the Foreign Relations Committee, where major constituencies include people with good historical reason to hate Nazis. (Yes, you can read that as “It’s tough to run the Foreign Relations Committee without backing from pro-Israel Jewish groups.”)

With a capital ‘T’

But there’s something deeper going on here that spells trouble for Trump.