They technically can bring charges -- to the president. It's impeachment. For folks other than the president the investigations is just for fact gathering purposes, which could result in the executive or the FBI or DOJ doing something.
http://www.let.rug.nl/usa/outlines/...ess/congressional-powers-of-investigation.php
Comey: We're freaked about the
timing of the firing. If he was fired for re-opening Hill's investigation, we'd be chill. But he was fired by Trump after he was onto something about Trump's ties to Russia. It's less about James Comey the man being fired and more about the FBI Director investigating possible Russian ties to the president being fired.
I can't say that without a doubt that she obstructed justice because I am not a legal scholar, but considering the FBI and DOJ haven't brought charges, I think it's clear how legal minds evaluated the case.