i can't even guess as to why they went quiet. not one guess at all. we will never know.
edit: well they're not quiet now once they get called out
The problem with Democrats is that they see someone as evil as Trump, and their response isn't, "damn, that is an evil man. We should put that man in prison." Their reaction is, "damn. Look how evil that man is. Wait, this means we can get away with being incredibly evil ourselves! As long as we are slightly less corrupt and evil than him, we can shame people into voting for us!"
They viewed Trump as an excuse for their own misbehavior rather more than anything else.