(verb)
: to assail by words or arguments : oppose or attack as false or lacking integrity
“Terrible people hire good attorneys every day. Gripe with malfeasance by said legal teams, sure, but to impugn a lawyer for literally doing his job is unconscionable.” — Tiana Lowe, The Washington (D.C.) Examiner, 13 May 2019
https://www.merriam-webster.com/word-of-the-day/impugn-2019-12-14