WASHINGTON — President-elect Trump and President Biden both pledged a smooth transition between administrations as they met at the White House on Wednesday morning. 

"I look forward… to having a smooth transition. We'll do everything we can to make sure you're accommodated, what you need," President Biden said as cameras and reporters were briefly allowed in the Oval Office for the meeting.

Speaking second, Trump emphasized that "politics is tough and in many cases it’s not a very nice world, but it is a nice world today."

"I appreciate very much the transition that's so smooth. It will be as smooth as it can get, and I very much appreciate that," the former and future president added.

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President Biden, right, shakes hands with President-elect Trump in the Oval Office of the White House in Washington, D.C., on Wednesday.

President Biden, right, shakes hands with President-elect Trump in the Oval Office of the White House in Washington, D.C., on Wednesday. (AP Photo/Evan Vucci)

Trump returned to 1600 Pennsylvania Avenue just over a week after his sweeping election victory as he made his first stop back at the White House in nearly four years. He arrived at the White House at the invitation of Biden, the politician he knocked out of the 2024 presidential race.

For Biden — who ended his own re-election bid in July, a month after his disastrous debate performance against Trump reignited questions over whether the 81-year-old president was physically and mentally up for another four years in the White House and sparked calls for him to drop out of the race — the meeting with his predecessor and now successor was likely awkward.

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Trump spent years verbally eviscerating Biden and his performance in the White House. And even after Biden ended his re-election bid, Trump continued to slam the president and his successor atop the Democrats' 2024 ticket, Vice President Kamala Harris.

President Biden, right, meets with President-elect Trump in the Oval Office of the White House in Washington, D.C., on Wednesday.

President Biden, right, meets with President-elect Trump in the Oval Office of the White House in Washington, D.C., on Wednesday. (AP Photo/Evan Vucci)

And Biden, for a couple of years, has labeled Trump a threat to the nation's democracy.

But Biden, a traditionalist, wants to ensure a smooth transition between administrations.

Biden's offer to Trump to visit the White House was an invitation he himself was never accorded.

Four years ago, in the wake of his election defeat at the hands of Biden, Trump refused to concede and tried unsuccessfully to overturn the results.

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Breaking with longstanding tradition, Trump didn't invite Biden to the White House. And two weeks after the Jan. 6, 2021, attack on the U.S. Capitol by Trump supporters aiming to upend congressional certification of Biden's Electoral College victory, Trump left Washington ahead of the presidential inauguration of his successor, becoming the first sitting president in a century and a half to skip out on a successor's inauguration.

"President Biden met with President-elect Trump for approximately two hours in the Oval Office. White House Chief of Staff Jeff Zients and incoming Chief of Staff Susie Wiles joined the meeting," White House Press Secretary Karine Jean-Pierre told reporters Wednesday. "It was a substantive meeting and exchange of views. They discussed important national security and domestic policy issues facing the nation and the world. 

"President Biden also raised important items on Congress's to-do list for the lame duck session, including funding the government and providing the disaster supplemental funding the president requested," she continued. "Finally, the president reiterated what he said to the president elect the day after the election and to the American people in the Rose Garden just last week – we will have an orderly transition and a peaceful transition of power. "

National Security Advisor Jake Sullivan added that "President Biden reinforced his view that the United States standing with Ukraine on an ongoing basis is in our national security interest, and it's in our national security interest because a strong Europe, a stable Europe, standing up to aggressors and dictators and pushing back against their aggression is vital to ensuring that we don't end up getting dragged directly into a war, which has happened obviously twice in the 20th century on the European continent." 

A veteran political scientist pointed to the significance of the meeting.

"President Biden's decision to welcome President-elect Trump to the White House is a tribute to normalcy in the presidential transition process. What was denied to Joe Biden following his election is being restored to Biden's credit," veteran political scientist Wayne Lesperance told Fox News.

President Biden, right, meets with President-elect Trump in the Oval Office of the White House in Washington, D.C., on Wednesday.

President Biden, right, meets with President-elect Trump in the Oval Office of the White House in Washington, D.C., on Wednesday. (AP Photo/Evan Vucci)

Lesperance, the president of New Hampshire-based New England College, called the invitation by Biden " a remarkable gesture in that it legitimizes Trump's return to power by the nation's leading Democrat and, hopefully, will be met with a commitment to orderly transitions in the future."

The meeting was the first between Biden and Trump since they faced off in Atlanta on June 27 in their one and only debate.

The two presidents — along with Harris and Trump's running mate and now vice president-elect, Sen. JD Vance, R-Ohio, — also stood next to each other on Sept. 11 in New York City's Lower Manhattan at ceremonies for the 23rd anniversary of the 9/11 terrorist attacks.

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This was Trump's second meeting at the White House with a departing president.

Eight years ago, after defeating Democratic nominee Hillary Clinton, Trump sat down at the White House with President Obama, who was finishing up his second term steering the nation.

"We now are going to want to do everything we can to help you succeed. Because, if you succeed, then the country succeeds," Obama told Trump at the time.

While a tradition, the meeting between the incoming and outgoing presidents is not mandated.

Fox News' Sarah Tobianski and Greg Norman contributed to this report.