Senate Minority Leader Mitch McConnell, R-Ky., celebrated his 16 years as party leader with a Senate floor speech looking back at other leaders and their different styles. Jose Luis Magana/Associated Press

WASHINGTON — Democrats are again claiming the Senate majority, but much of the chamber’s focus Tuesday was on the top Republican as Mitch McConnell became the longest-serving Senate leader in history.

McConnell, 80, surpassed Montana Sen. Mike Mansfield’s record of 16 years as party leader when the Senate convened midday to begin the new Congress. While the Kentucky Republican has acknowledged he would prefer his own party to be taking charge – “the majority is better,” he says frequently – he celebrated his own personal milestone with a Senate floor speech looking back at party leaders and their different styles over the decades.

And Senate Majority Leader Chuck Schumer, D-N.Y., cemented a legacy of his own after winning a second term as leader and also being sworn in as the longest-serving senator from New York. Democrats will go into the new Congress with a 51-49 majority, with newly Independent Sen. Kyrsten Sinema receiving her committee assignments from Democrats.

The celebratory Senate proceedings were in marked contrast to the new Republican House majority across the Capitol, where Republican Leader Kevin McCarthy is fighting to become speaker amid contentious internal strife in his own party. McConnell, his party’s leader since 2007, easily dismissed a similar challenge from within after the November midterms, and, like Schumer, begins the new year with strong support from his caucus.

Similar to President Biden, both Schumer and McConnell are opening the year pledging to work across the aisle – and all three will have to find ways to work with the new GOP House majority to keep government running. McConnell will make a rare appearance with Biden in his home state of Kentucky this week to highlight nearly $1 trillion in infrastructure spending that lawmakers approved on a bipartisan basis in 2021.

Claiming his party’s majority after senators were sworn in, Schumer said that party differences “do not absolve either either side of the need to work together when the good of the country is on the line.”

“Whoever ends up becoming speaker of the House, I hope they will find a way to work with us in a productive way this Congress,” Schumer said, as McCarthy failed to secure a majority in three rounds of voting and the House postponed further proceedings until Wednesday.

Praising the tenure of Mansfield, a Democrat who led his party from 1961 to 1977, the ever-restrained McConnell hinted at his own long-term strategy – a contrast to the bombast and chaos across the Capitol.

“There’ve been leaders who rose to the job through lower-key, behind-the-scenes styles; who preferred to focus on serving their colleagues rather than dominating them,” McConnell said in his floor speech, and that “is how Senator Michael Joseph Mansfield of Montana became the longest-serving Senate leader in American history until this morning.”

Without directly comparing himself to Mansfield, McConnell appeared to draw similarities between their styles, saying that Mansfield knew how to work the Senate and “contented himself with the modest task of keeping the Senate machinery oiled” while other senators with “stronger and clearer visions championed particular outcomes.”

Also Tuesday, the Senate swore in seven new members, five Republicans and two Democrats. Unlike the House, where the swearing in was overshadowed by the antagonistic fight over the speaker’s chair, the mood was jovial in the Senate. Family, friends and predecessors looked on as those freshman, along with their new colleagues who won re-election, took an oath of office administered by Vice President Kamala Harris.

Senators clapped as Illinois Sen. Tammy Duckworth, a Democrat and Iraq War veteran who lost both legs when her helicopter was shot down in 2004, walked down the center aisle of the Senate to be sworn in instead of using her wheelchair – leaning on her Illinois colleague, Sen. Dick Durbin, for support. Former Republican Sen. Frank Murkowski of Alaska accompanied his daughter, newly re-elected Alaska Sen. Lisa Murkowski, and hugged her after she took her oath. Ohio Sen. Sherrod Brown, a Democrat, stood behind newly elected Republican Sen. J.D. Vance of Ohio, a rare show of bipartisanship on swearing-in day.

John Fetterman, a Pennsylvania Democrat, is the only new senator who flipped party control of his seat, having won an open seat held by retiring Republican Sen. Pat Toomey. The other six new senators are all replacing retiring members of the same party.

New Republican senators are Ted Budd of North Carolina, Katie Britt of Alabama, Markwayne Mullin of Oklahoma, Eric Schmitt of Missouri and Vance of Ohio.

Vermont’s Peter Welch is the only other new Democrat, replacing Sen. Patrick Leahy, who is retiring after almost five decades in the seat. “I’m looking forward to getting to work,” Welch said as he walked onto the Senate floor to be sworn in.

Washington Sen. Patty Murray made her own history, replacing Leahy as the first woman Senate president pro tempore. That position is held by the senior-most member of the majority party and is third in line to the presidency.

“I’m honored to officially become the President Pro Tempore of the Senate today,” Murray tweeted after she took her oath, Leahy standing behind her. “It’s not lost on me the significance of what it means to be the first woman to serve in this role. This is another sign that slowly but surely, Congress is looking more like America.”

Biden tweeted his congratulations to Murray: “We’re witnessing history on Capitol Hill,” he said.

Associated Press writer Seung Min Kim contributed to this report.