Late Wednesday morning, President Trump headed into what was supposed to be a meeting with congressional Democrats on how to fund a $2 trillion infrastructure package he and they had agreed on last month. Instead, he spent three minutes berating Democratic leaders for saying unpleasant things about him, before proclaiming that he would not work with them until they stopped investigating him.

Mr. Trump then strode out to the Rose Garden, where the news media had been hastily assembled to hear him deliver a similar message, and delivered another tirade about the illegitimacy of the special counsel’s Russia investigation. “This whole thing was a takedown attempt at the president of the United States,” he asserted. Affixed to his lectern was a printed sign declaring, “NO Collusion. NO Obstruction.”

The proximate cause of Mr. Trump’s outrage was an accusation by the House speaker, Nancy Pelosi, made earlier in the day, that he “is engaged in a cover-up.”