Impeachment may present a greater problem for Susan Collins than for Trump, because it leaves her with two lousy options. If she ultimately votes to convict, the Trumpist right in Maine will be outraged, and she needs every vote she can get in 2020; on the other hand, if she votes to acquit, she will lose swing voters that she also needs, and she will be sending the message for all time that selling foreign policy for private gain is OK. It’s an unappealing menu, to say the least.
So what does she do? Trump will probably survive with or without her support, and the Trumpist right has nowhere else to go. If I were in her position, I would view a vote for conviction as the better option. Of course, she could try to find middle ground by acquitting, but supporting some sort of censure motion, but that is unlikely to satisfy anyone.