Donald Trump’s campaign manager, Corey Lewandowski, listens at left in Palm Beach, Fla., on March 15. (Gerald Herbert/Associated Press)

POLITICAL CAMPAIGNS are sometimes derided for their stage management, but they can offer moments of clarity about the character of a candidate. The charging of Donald Trump’s campaign manager, Corey Lewandowski, with simple battery, a misdemeanor, is one such moment.

How did Mr. Trump react when one of his key campaign aides apparently manhandled a reporter and then denied having done so? Instead of the rigorous fact-finding and dispassionate thinking that should be prerequisites for the Oval Office, there was denial and doubling down.

Police in Jupiter, Fla., charged Mr. Lewandowski on Tuesday in connection with a much-publicized March 8 incident involving Michelle Fields, then a reporter for Breitbart News. Ms. Fields said she was trying to ask Mr. Trump a question when she was roughly grabbed and yanked down by Mr. Lewandowski. She had bruises on her arm, and her account was corroborated by Post reporter Ben Terris.

A mature and respectful campaign would have responded with an acknowledgment and apology, which likely would have ended the matter. Instead, Mr. Lewandowski called Ms. Fields “totally delusional,” tweeting, “I never touched you. As a matter of fact, I have never even met you.” For his part, Mr. Trump made a show of backing Mr. Lewandowski, making sure Mr. Lewandowski was onstage during his victory speech at the Mar-a-Lago resort after the March 15 primaries.

Even after Jupiter police investigated the complaint filed by Ms. Fields, brought the misdemeanor charge and posted a video showing Mr. Lewandowski with his hands on Ms. Fields, Mr. Trump refused to back down. “Wow,” he tweeted Tuesday, “Corey Lewandowski, my campaign manager and a very decent man, was just charged with assaulting a reporter. Look at tapes — nothing there!” Mr. Lewandowski says he will plead not guilty.

We second Mr. Trump’s advice: Do look at the tapes. That Mr. Trump sees nothing wrong confirms the troubling lack of judgment that he has demonstrated repeatedly. The brazen willingness to overlook fact and evidence, and the ease with which he countenances the smearing of a victim — these are not compatible with a presidential temperament.