Nicolle Wallace, who was a spokeswoman for President George W. Bush, said she considered Mr. Epshteyn a friend and admired his political skills. “He is everything you want in a surrogate because he believes in his candidate,” said Ms. Wallace, now a political analyst for MSNBC.

Others have found his manner, which can quickly accelerate from reasonable to aggressive to dismissive, off-putting. He also has let his emotions get the better of him.

Two years ago, Mr. Epshteyn was charged with misdemeanor assault in Scottsdale, Ariz., after a bar fight. The charge was dropped after he agreed to undergo anger management counseling and perform community service.

“Boris takes a certain amount of delight in trying to bully the interviewer,” said Joy Reid, the host of a show on MSNBC, who has clashed with Mr. Epshteyn. “He sees every night as combat and he goes in as very combative.”

Three political commentators said in separate interviews that he often acted in a rude, condescending manner toward show staffers, makeup artists and others. The three, all of whom are opposed to Mr. Trump’s election, spoke on condition of anonymity because they sometimes appear on air with Mr. Epshteyn.

“Boris is abrasive,” Ms. Reid added. “That is who he is both on the air and off.”

Mr. Epshteyn said in an email that he absolutely disagreed with such remarks. ”I have utmost respect for all of the great people I have the pleasure to come in contact with,” he wrote.

Image Boris Epshteyn

A Trump campaign spokesman, Jason Miller, declined to make Mr. Epshteyn available for an interview.

“Boris Epshteyn is a tireless and effective advocate for our campaign,” Mr. Miller said in a statement, adding that he was “a positive influence for those helping to change” the country’s direction.