“Are you talking to me?” President Trump asked, his brow creased in disgust.

He was staring at Jeff Mason, a Reuters reporter whom Mr. Trump had called on moments earlier during an East Room news conference with the president of Finland.

Such events, with the American president joined by a fellow head of state, are usually formal affairs. But Mr. Trump seemed to be in a stormy mood on Wednesday, lashing out on Twitter and in person at his enemies, real and perceived, as House Democrats pursue a formal impeachment inquiry against him.

One regular Trump boogeyman — the American news media — has come in for particular ire of late. Mr. Trump has tweaked his usual “fake news” sobriquet, now preferring the term “corrupt news.” Earlier on Wednesday, in the Oval Office, he attacked the credibility of The Washington Post over an article that outlined his interest in constructing an alligator- and snake-filled moat along the southern border. Mr. Trump appeared unaware that the article had been published by The New York Times.

Then came the exchange with Mr. Mason, which was emblematic of the president’s escalating attacks on the press.