This alone is a 100% impeachable offence. It's a massive crime to retaliate against a witness.
18 U.S. Code § 1513. Retaliating against a witness, victim, or an informant
(e) Whoever knowingly, with the intent to retaliate, takes any action harmful to any person, including interference with the lawful employment or livelihood of any person, for providing to a law enforcement officer any truthful information relating to the commission or possible commission of any Federal offense, shall be fined under this title or imprisoned not more than 10 years, or both.
It's going to be amazing to see what he does and gets away with before November.