Republicans know that too, but they also know this is something they can make Dems flinch and equivocate about, which makes them look overall weak and indecisive. They did it with immigration last cycle, they did it with gay marriage 20 years ago. The only way to win is to tell them to eat shit
I have to keep saying this. Trans rights are very unpopular on face but extremely sensitive to persuasion and question wording. In other words very few people care deeply about them, one way or another. Electorally, there is no advantage or penalty for Democrats to take one way or another.