Here's the problem - If Collins opposes it, she knows the Democrats will run someone against her when she's up for re-election. Doesn't matter how many times she has sided with Democrats, and I'm sure she's going to whine and say "but...but...I was bipartisan and worked with Dems" but the Dems don't care about that crap. Just like they targeted Lincoln Chaffee they're going to target the RINOs. And conservatives won't be around to help them.
Even FDR mocked me-too Republicans who sat there sniveling for Democrat's affection.
80 % of the general public is still 60 % of Maine. Almost nobody who's voted for her will mind if she votes against it. OTOH, she's not the sharpest knife in the drawer..
OTOH again, I doubt Nelson (Dem) of Nebraska will go for this. As for the others, I can't say I know for sure, but small business lobbies will go ballistic if this thing passes.