Donald Trump returned to Washington on Tuesday for the first time since leaving the White House 18 months ago, delivering a fiery speech sprinkled with strong hints he may run for president again in 2024.

The 76-year-old stopped short of declaring his candidacy, but laid out what he believed should be the priorities for the "next Republican president."

"I always say I ran the first time and I won, then I ran a second time and I did much better," Trump said. "We may just have to do it again. We have to straighten out our country.

"I look forward to laying out many more details in the weeks and months to come."

Several hours before Trump took the stage at the right-wing America First Policy Institute, his former vice president, Mike Pence, who is also considering a White House run in 2024, addressed a different conservative audience in Washington.

Speaking at the Young America's Foundation conference, Pence said Americans must look to the future not the past and played down differences with Trump.

"Elections are about the future," Pence said. "I came today not to look backwards but to look forward.

"I don't know that the president and I differ on issues," he said. "But we may differ on ­focus."

Trump's 90-minute address to the conservative America First Policy Institute echoed many of the themes of his victorious 2016 campaign, including illegal immigration and crime.

Trump repeated his false claims that he won the 2020 election and denounced the House committee investigation into the January 6, 2021 attack on the US Capitol by his supporters as the work of "political hacks and thugs."

"If I renounced my beliefs, if I agreed to stay silent, if I stayed at home and just took it easy, the persecution of Donald Trump would stop immediately," he said. "But that's not what I will do. I can't do that.

"They really want to damage me so I can no longer go back to work for you," he said.

"And I don't think that's going to happen," he added, prompting chants from the crowd of "Four more years!"

Trump lashed out repeatedly at Democratic President Joe Biden, blaming him for the country's ills.

"We are a nation in decline," Trump said. "We are a failing nation."

He accused Biden of allowing an "invasion" by millions of migrants crossing the southern border.

Trump said the US "is now a cesspool of crime."

"We have blood, death and suffering on a scale once unthinkable," he said. "Democrat-run cities are setting all-time murder records."

Since taking his last Air Force One flight from Washington to Florida on January 20, 2021, Trump has remained the country's most polarizing figure, continuing his unprecedented campaign to sow doubts about his 2020 election loss to Biden.

For weeks, Washington has been riveted by hearings in Congress about the storming of the Capitol by a Trump mob and his attempts to overturn the election.