WASHINGTON — Democrats passed 250 seats in the U.S. House of Representatives on Thursday, cementing the largest Democratic House majority in nearly two decades and setting up a historic leadership team to take charge when the 120th Congress convenes on January 3.

The milestone came as the party's expected leadership took shape in public. Rep. Hakeem Jeffries of New York formally asked House Democrats for their support this week, putting him in line to become the first Black speaker of the House, while Rep. Katherine Clark of Massachusetts officially declared her candidacy for majority leader on Thursday.

Jeffries introduced Clark at a news conference on Wednesday as "the next majority leader of the House of Representatives" and "someone who will be the first woman to ever serve in that position in our 250-year journey." Clark, 63, the current House minority whip from Revere, has served in Congress since 2013.

"In the words of the great Dolly Parton, it's been a long hard fight, but I see a brand new day a-dawning," Clark said, adding that Americans had entrusted Democrats "to lead us forward to something better, to make their lives easier."

In a letter to colleagues announcing her bid, Clark wrote that her priority would be "ensuring that every corner of our Caucus is heard and empowered to have a role in the policymaking process." She is unopposed so far, and House Democrats are scheduled to hold leadership elections on November 18 and 19.

If elected, Clark would become the second-ranking member of House leadership, behind the speaker. The full House will vote on the speakership on January 3, when the new Congress is sworn in.