So basically - it's a political "witch-hunt" by the Democrats?

To a point.  One would still need some legal footing...what is happening now seems to be a concerted effort by Democrats to grasp at anything to influence the midterm elections.  However, even Pelosi is warning the Dems to back off a bit - that "Trump fatigue" could backfire.  And the influence on the midterm elections is not going to change the control of Congress in 2018 anyway.