The Democrats do have another option, and I haven’t seen it mentioned _anywhere_ (which means it could happen ;-) ).
They could vote to censure Trump—sorta mollifies the base, but does not require Senate hearings....
Remember this post—if I called it I want a FR participation trophy!
They could vote to censure Trump
They could...
But as you say, their base would not be satisfied with this and President Trump would wear it as a BADGE OF HONOR.