WASHINGTON — President Trump warned evangelical leaders Monday night that Democrats “will overturn everything that we’ve done and they’ll do it quickly and violently” if Republicans lose control of Congress in the midterm elections.

Speaking to the group in the State Dining Room of the White House, Mr. Trump painted a stark picture of what losing the majority would mean for the administration’s conservative agenda, according to an audiotape of his remarks provided to The New York Times by someone who attended the event.

“They will end everything immediately,” Mr. Trump said. “When you look at antifa,” he added, a term that describes militant leftist groups, “and you look at some of these groups, these are violent people.”

A White House spokesman, Hogan Gidley, declined to elaborate on what the president meant.

The blunt warning — delivered to about 100 of the president’s most ardent supporters in the evangelical community — was the latest example of Mr. Trump’s attempts to use the specter of violence at the hands of his political opponents and to fan the flames of cultural divisions in the country.