Committees of Congress cannot charge people with crimes.
Yes, of course, but they can help President Trump in a politically risky situation by charging Rosenstein and possibly Sessions with contempt of Congress for slow walking and redacting and even now directly refusing a subpoena. That would be a valuable support for the President, politically, to him to go ahead and fire some folks. More directly, the heads of the relevant committees could even recommend firings, based on the obstruction, and in Rosenstein’s case, even hiring Mueller in the first place and Rosenstein's multiple conflicts of interest.