Impeachment of the president is justified on constitutional grounds if any of the following 12 questions is answered in the affirmative:

Memo to Congress: Impeachment probe needed now!

If the president is not guilty of any of these crimes, then a thorough investigation by a House committee with subpoena power will clear the air. If he is guilty, then the U.S. House of Representatives has a moral obligation to vote for a resolution of impeachment, and the U.S. Senate must bring him to trial.