So much for defanging the poisonous debate in Washington.

Dozens of congressional staffers erupted into boos, jeers and even vulgar gesticulations Thursday when President Trump appeared in a video at the Congressional Baseball Game at Nationals Park.

Mr. Trump delivered a message of unity, but some fans in the stands weren’t having any of it.

One man shouted an expletive at the video screen as Mr. Trump was telling the fans: “We are showing the world we will not be intimidated by threats.”

The episode marred what had been a night celebrating those wounded in Wednesday’s murderous attack on GOP players practicing for the game.

When both teams went to second base — the symbolic spot where Rep. Steve Scalise was wounded in the attack at the Alexandria practice field — to kneel and pray, some mocked the prayer, too. The fans appeared to be Democratic staffers, having booed the announcement of several members of the GOP lineup.