It is the DUTY, not the option of Congress to investigate presidents who may have broken the law of the Constitution.
There is nothing in the Constitution that makes this action dependent on a future election, a possible failure to gather enough votes for an indictment or anything else.
All elected officials take an oath to uphold the Constitution. Allowing a criminal president to escape the consequence of their misdeeds is no different than a prosecutor deciding to not prosecute a murderer because the jury may not find the alleged killer guilty.
It is clear to most citizens that Congress is negligent in not investigating the alleged high crimes of Cheney and Bush. The evidence is clear and plentiful and also whether we go on as a Democracy or as a Fascist dictatorship hangs in the balance.
Since there is collusion in the DOJ with lack of investigation and stonewalling impeachment is the only way to get at the truth. Writing nice letters has gone on long enough. Even if Congress doesn't impeach, the investigation will let all America what is going on so we can decide.
If any Democrat wants to be reelected they had better do their job or start looking for other work.
At this moment I am no longer a Democratic donor and plan to try my best to unseat any incumbent Congress-person. Since I believe in the Democratic ideals that have been forgotten I will reconsider when I see real Democrats at work showing me their main concern is America.