"Donald, congratulations," Biden said, greeting Trump with a handshake and adding that he looked "forward to a smooth transition."

Trump made a similar pledge and expressed thanks to Biden for the invitation -- one that Trump himself had not extended to Biden after losing the 2020 election.

"Thank you very much," Trump said. "Politics is tough. And it's, in many cases, not a very nice world. But it is a nice world today and I appreciate it very much."

Trump, flying from Florida, arrived at a military base near the Capitol, meeting up with billionaire Elon Musk for a morning session with House Republicans as Trump prepares for a potentially unified Republican government and sweep of power.

Back in Washington for the first time since his election victory, Trump told the GOP lawmakers, "It's nice to win."

Trump received a standing ovation from House Republicans, many of whom took cellphone videos of him as ran through their party's victories up and down the ballot, in what would be, under the constitutional limits, his final presidential election.

"I suspect I won't be running again unless you say he's good we got to figure something else," Trump said to laughter from the lawmakers.

It's a stunning return to the U.S. seat of government for the former president, who departed nearly four years ago a diminished, politically defeated leader after the Jan. 6, 2021 attack on the Capitol but is preparing to come back to power with what he and his GOP allies see as a mandate for governance.

"He is the comeback king," said House Speaker Mike Johnson, R-La., before Trump's arrival. "We owe him a great debt of gratitude."

The private meetings, including his sit-down with Biden, put in stark relief the former president's comeback. Trump's reemergence comes amid Republican congressional leadership elections, with the potential for him to place his imprint on the outcome.

Trump endorsed Johnson's return to the speaker's office with the president-elect saying he is with Johnson all the way, according to a person familiar with the remarks but not authorized to publicly discuss the private meeting.

Musk has been spending much of his time at Mar-a-Lago, Trump's Florida estate, and participating in discussions as the incoming Trump administration prepares to transition from Biden's.

The Tesla and SpaceX CEO, was named by Trump to a government efficiency advisory role. Musk, Some close to Trump and his team now see Musk as the second most influential figure in Trump's immediate orbit, after Susie Wiles, the campaign manager who is Trump's incoming chief of staff.

Johnson has said Republicans are "ready to deliver on Trump's "America First" agenda.

After his election win in 2016, Trump met with President Barack Obama in the Oval Office and called it "a great honor." But he soon was back to heaping insults on Obama, including accusing his predecessor -- without evidence -- of having wire-tapped him during the 2016 campaign.

Four years later, Trump disputed his election loss to Biden, and he has continued to lie about widespread voter fraud that did not occur. He didn't invite Biden, then the president-elect, to the White House and he left Washington without attending Biden's inauguration. It was the first time that had happened since Andrew Johnson skipped Ulysses S. Grant's swearing-in 155 years ago.

Biden insists that he'll do everything he can to make the transition to the next Trump administration go smoothly. That's despite having spent more than a year campaigning for reelection and decrying Trump as a threat to democracy and the nation's core values. Biden then bowed out of the race in July and endorsed Vice President Kamala Harris to succeed him.

In the wake of the election, the president has abandoned his dire warnings about Trump, saying in a speech last week, "The American experiment endures. We're going to be OK."

Traditionally, as the outgoing and incoming presidents meet in the West Wing, the first lady hosts her successor upstairs in the residence, But her office said Melania Trump wasn't attending, saying in a statement that "her husband's return to the Oval Office to commence the transition process is encouraging, and she wishes him great success."

When Trump left Washington in 2021, even some top Republicans had begun to decry his role in helping incite a mob of his supporters that had staged the violent attack on the Capitol mere weeks earlier, trying to stop the certification of Biden's election victory.

But his win in last week's election completes a political comeback that has seen Trump once again become the unchallenged head of the GOP.

Wednesday's trip was not the first time Trump has returned to the Capitol area since the end of his first term, though. Congressional Republicans hosted Trump over the summer, as Trump was again solidifying his dominance over the party.

His latest visit comes as Republicans, who wrested the Senate majority from Democrats in last week's elections and are on the cusp of keeping GOP control of the House, are in the midst of their own leadership elections happening behind closed doors Wednesday.

The president-elect's arrival will provide another boost to Johnson, who has pulled ever-closer to Trump as he worked to keep his majority -- and his own job with the gavel.

The speaker said he expects to see Trump repeatedly throughout the week, including at an event later that evening, and at the president-elect's Mar-a-Lago estate in Florida "all weekend."

It's unclear whether Trump will also visit the Senate, which is entangled in a more divisive closed-door leadership election in the three-way race to replace outgoing GOP Leader Mitch McConnell.

Trump's allies are pushing GOP senators to vote for Sen. Rick Scott of Florida, who had been a longshot candidate challenging two more senior Republicans, Sen. John Thune of South Dakota and Sen. John Cornyn of Texas, for the job.

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Associated Press writers Jill Colvin in New York and Farnoush Amiri, Zeke Miller, Darlene Superville and Kevin Freking contributed to this report.