Not sure that I interpret Kristol's tweets as American Thinker does. Sounds to me like he is doing what a number of other Never Trump conservatives have said they will do -- vote Democrat in November because they can't in all good conscience vote for Trump. It's not they are officially switching parties for good.
I've had a few suggest this approach to me since I won't vote for Trump. But I can't in all good conscience vote for a Democrat either. Even the so-called centrists, such as Biden, will sooner or later adopt the radical politics of the ultra left because that is where the Democrat Party is headed. Unfortunately, the Republican Party is also moving left. Should the Democrats take the senate as well as the house, expect Republicans to move even further left to hold onto voters. Those of us who are real conservatives will not have anyone to represent us.
Not a fan of Kristol, but I believe I understand where he is coming from. He's not alone in his frustration. I just don't know that I would vote for the ones whose policies are everything contrary to the republic our Founding Fathers created just because I don't like the guy in the White House. It's kind of like cutting off one's nose to spite one's face and just as bad as voting for Trump to "save us" from the Democrats. Neither idea is a good one and can actually make matters worse.