To challenge as false, cast doubt upon.
“This was a great N.Y.P.D. officer who dedicated himself—put his life in harm’s way hundreds of times during his career—and you can use your own definition,” Mr. [Michael R.] Bloomberg said at a news conference in Brooklyn when asked if he regretted his earlier comments. “It’s a question of how you want to define what a hero is, and certainly I did not mean to hurt the family or impugn his reputation.”
—Diane Cardwell ”Mayor Backs Away From Questioning Dead Officer’s Heroism” New York Times, October 31, 2007