This one strikes me as tricky even in theory.

Sure, in theory the democrats have a majority in the house, but they likely won't even have a simple majority in the senate, and if they are anything short of 2/3rds majority in the senate, it's largely moot. They can't pass anything Trump doesn't want and they can't remove Trump from office. Yeah, they are supposed to have leverage to deny legislation, but this administration has proven itself quite happy to unilaterally act..