Donald Trump’s smearing and threatening of witnesses, whistleblowers, and investigators are crimes.
US federal law — specifically 18 US Code § 1512. Tampering with a witness, victim, or an informant — prohibits any effort to intimidate, threaten, corruptly persuade, or engage in misleading conduct toward (e.g. smear and defame) a witness or whistleblower.
(b) Whoever knowingly uses intimidation, threatens, or corruptly persuades another person, or attempts to do so, or engages in misleading conduct toward another person, with intent to—
(1) influence, delay, or prevent the testimony of any person in an official proceeding;
“Misleading conduct” may include not only smearing and defaming witnesses but also giving false instructions based on legally unfounded claims of executive privilege, blanket immunity, or other powers and privileges that do not exist in law.
It is unlawful for any person to use public office in any manner to assist, condone, or protect President Trump or any of his allies in their criminal efforts to intimidate, menace, or otherwise tamper with the behavior and testimony of witnesses.