There is no indication that Trump thought he could "wipe the floor" with Bernie. In fact, it was likely the opposite. The polling certainly didn't agree, for whatever that's worth. Even if he did think that, there is no indication that he would have been right. It's funny how Trump is an evil genius when the Democrats want him to be that, and a raging moron when they want that.
Once Bernie was put up against Trump rhetorically, Bernie's lead would have grown substantially. Bernie talks to a huge segment of America that most Democrats talk past. Most Democrats don't even get heard because they have nothing worthwhile to say.
I can't believe I'm playing defense for MTG but, voting for the bill in the House was a low risk action because there was absolute certainty that there would have to be back and forth with the Senate. The vote in the house was basically a vote to get the process started in the Senate.
The bill as a whole though is still absolute shit stuffed with one horror after another. I do hold everyone who voted for it responsible for that. I just don't think it's a big deal that she voted for some specific aspects that she later opposed. That's just how the process of Omnibus bills works.