Do you think they've ever considered for a moment that the DOJ isn't investigating what they want because there's not enough evidence to warrant it? If DOJ thought there was, they'd be on it instead of waiting for Congress to act as their investigative arm. Congressional investigations, like impeachment, are POLITICAL acts, not law enforcement acts. Clinton was impeached because it had already been established that he broke the law by lying under oath, not because "we don't like him, so he must be guilty of sumthin'."
During the four-year-long rolling insurrection by the Left during Trump's presidency, we had sitting members of Congress standing in the well and before raucous crowds, not calling for peaceful demonstrations like Trump did, but exhorting mobs already rioting to become even more "active" and confrontational and to harass their political opponents. Chris Cuomo was asking, "Who said protests were supposed to be peaceful?", and Democrat mayors were issuing stand down orders to police while their cities burned and their citizens were terrorized.
If you want to investigate something for the sake of justice, investigate that.
