Ms. Lee, 72, said afterward that she "absolutely" saw ageism and sexism at work.
"That's something women, especially women of color and African-American women, have to fight constantly, every and every day," she said, adding, "We still have many glass ceilings to break."
Mr. Jeffries, in response, called the race "a friendly contest of ideas." Inside the auditorium where elections were held, one of his backers, Representative Juan C. Vargas of California, likened him to another black Democrat with an unusual name and a gift for oratory: former President Barack Obama.
"When I got to Congress, my wife asked me if there was anyone in Congress that reminded me of Barack Obama, and I said, 'Yeah, there's this guy Hakeem Jeffries from Brooklyn, I think he's the next guy,'" Mr. Vargas said, according to one person in the room.
Mr. Jeffries, the son of a social worker for the city and a worker for the city of New York, has a master's degree in public policy from Georgetown University and a law degree from New York University, and worked as a corporate lawyer, including for CBS, before entering politics. He won his first race in 2006, securing a seat in the New York State Assembly after two unsuccessful attempts. In 2012, he was elected to the Congress.
Mr. Jeffries has long been on the political radar in New York; In 2015, he was talked about as a possible candidate for mayor, though he made clear at the time that he preferred to stay in the House.
Here in Washington, he is known as a fierce and fiery critic of President Trump; after racial violence erupted last year in Charlottesville, Va., he accused Mr. Trump of playing "political footsie" with the former Ku Klux Klan leader David Duke, telling CNN, "It's time for him to stop acting like a two-bit racial hustler and start acting like the president of the United States of America."
But while he is progressive, he is also a pragmatist, and is considered to be in the deep divisions that have erupted in the Democratic caucus between the ascendant left and the so-called red-to-blue members, who flipped Republican seats in districts won by Mr. Trump.