I agree that this seems stupid. There is simply no way that Trump gets convicted in the Senate. I don't know if this is an attempt to force more testimony under oath that Dems hope they can use against him in the election, or just a misguided attempt to rile up the base. I have pretty much no faith in the House of Representatives at all (regardless of who is in charge) to hold themselves back from doing something ridiculous. That chamber has been completely off the rails for over a decade now.
Also - in the scheme of what is going on right now, the Clinton scandal seems downright quaint.