I will cheerfully allow people who voted for Trump and have been burned by him and now are anti-Trump to fight him all they want. I might even support them in doing so. But they haven't changed a bit. They've just found out after fucking around, and their new antipathy to him is just as selfish as their old support. I will not trust them, I will not welcome them, and I know that the second they get the chance they'll stick a knife in my back. They're still my enemy, but they're also my enemy's enemy and thus I will do what I can to make it easier for them to be a problem for my enemy. That's the cold calculus of it.
That's normal, everyday people. The people who sat in the halls of power? They're by and large grifters. They'll change their coat on a dime, and right now they see more influence and money to be made as members of "the resistance" or whatever. The Lincoln Project grifters are prime examples of this, but there are and will be plenty of others. Tell them to fuck off until they pay for what they've done, until they do more than say that they're against Trump now. Certainly don't give them any money or influence. Don't give them oxygen as far as I'm concerned. Ignore them. They'll go away.
I give ammunition to my enemy's enemy with enough safeguards that it can't be turned on me. That's all. Let them fight. They're no friends of mine.