CNN characterizes the endorsement as “upending Senate GOP plans”:

Cornyn has spent over a year courting Trump’s support, while Paxton has run to Cornyn’s right and pitched himself as a stronger ally of the president. Cornyn and Senate GOP leaders argued that he is a stronger general-election candidate as Democrats look to win statewide office in Texas for the first time since 1994.

The runoff is a week away, and early voting began Monday.

True that Cornyn would be stronger in the general? False? I am no expert on Texas politics, but it seems to me a tossup: Paxton appeals more to the base and Cornyn to the middle and is disliked by the base as a RINO. But Paxton is described as “scandal-plagued.” Then again, Lisa Murkowski supports Cornyn and says “she was ‘supremely disappointed’ and echoed leadership concerns that Paxton could have a harder time keeping the seat in GOP hands.” I suppose “leadership” means Thune? And of course, it’s Murkowski saying this, and I do not trust her to act in the GOP’s best interests..

The whole things seems like a mess:

Despite promising to intervene quickly after March 3, when Cornyn finished narrowly ahead of Paxton, Trump kept both campaigns on edge for months. He initially said he would ask his non-endorsed candidate to drop out, but his neutral stance meant the opportunity to do so came and went.

Instead, the two camps and their allies have spent nearly $25 million on advertising in the runoff, much of it used for the two candidates to bash each other in intensely personal terms. It brings the total ad cost of the Republican primary to nearly $125 million, most of which has come from the pro-Cornyn side.

Apparently Trump thinks that Talarico, the Democrat opponent, will be a weak candidate. I hope he’s correct. For what it’s worth (probably not all that much), polls indicate that both Republicans are more or less tied with Talarico at present.