As Impeachment Moves Forward, Trump’s Language Turns Darker

In the past, Mr. Trump has defined treason as a crime with “long jail sentences” and, during the special counsel investigation into his campaign’s ties to Russia, he brought up the case of Julius and Ethel Rosenberg, who were executed in 1953 after being found guilty of conspiracy to commit espionage.

“When they say ‘treason,’ you know what treason is?” Mr. Trump asked reporters in 2017 as he defended his son, Donald Trump Jr., against criticism that he had met with a lawyer connected with the Russian government at Trump Tower to gather dirt on Hillary Clinton. “That’s Julius and Ethel Rosenberg for giving the atomic bomb, O.K.?”

The Rosenbergs, who in fact were not convicted of treason, were prosecuted by Roy Cohn, a mentor of Mr. Trump’s. Mr. Cohn, who as a young aide to Senator Joseph McCarthy made his name by ensuring that the couple was sent to the electric chair, would later go on to coach Mr. Trump in the art of full-on assault of his enemies.

“He’s been vicious to others in his protection of me,” Mr. Trump said in 1980 of his mentor, who was eventually disbarred for “unethical,” “unprofessional” and “particularly reprehensible” conduct.

As Mr. Trump continues to emulate the bare-knuckle tactics he learned decades ago, he has alarmed Democrats who say his rantings against the whistle-blower will have a chilling effect in preventing people from coming forward in the future.

“This president’s comments about ‘spies and treason’ and ‘what we used to do in the old days’ are totally unacceptable and will do serious damage far beyond this news cycle,” Senator Mark Warner, Democrat of Virginia, said on Twitter on Monday. “The whole reason we have whistle-blower protections is so intelligence professionals can report wrongdoing without fear of retaliation.”

Representative Maxine Waters, a California Democrat who has long been targeted by the president at his rallies — taunts she has said have led to death threats — said on Tuesday that Republicans had not done enough to curb Mr. Trump’s behavior.