US President Joe Biden took his reelection message to a raft of key swing states Friday, buoyed by a combative, well-received State of the Union address that savaged rival Donald Trump.

Democrat Biden heads to Pennsylvania on Friday and Georgia on Saturday as the campaign for November's White House rematch with Republican former president Trump starts in earnest.

Next week the 81-year-old Biden heads to New Hampshire on Monday, Wisconsin on Wednesday and Michigan on Thursday, as he rides the momentum from his primetime speech.

Biden on Thursday launched one of the most scorching addresses ever seen from the podium of the House of Representatives, transforming what used to be a somber set-piece occasion into a raucous political rally.

He repeatedly attacked Trump for "bowing down" to Russian President Vladimir Putin and being a threat to US democracy, while assailing Republican lawmakers in the chamber as the former president's stooges.

The aim was also to ease concerns of skeptical voters about his age, with America's oldest president bringing the fight in an energetic performance that saw him spar with Republicans in exchanges sprinkled with jokes.

Flush with cash from donors, Biden's team said he would now campaign in every battleground state during March as he seeks to get the message across to voters.

- 'Decisive' -

Vice President Kamala Harris -- a visible presence behind Biden during the speech as she repeatedly stood and applauded the president -- is making trips to Arizona and Nevada focusing on Latino voters, it said.

"Joe Biden has made it his mission to reach voters where they are and bridge our divides," Campaign Chair Jen O'Malley Dillon said.

"While Donald Trump -- saddled with a losing agenda and a cash-strapped operation -- is actively alienating decisive voters."

Trump faces a financial squeeze as he battles multiple legal battles, including a criminal case for trying to overturn his 2020 election loss to Biden and a $355 million civil fraud fine.

Biden heads to Philadelphia for a campaign event on Friday, the latest in a series of visits in recent months to the crucial state of Pennsylvania.

Pennsylvania was one of the three "Blue Wall" states where largely working class voters abandoned the Democrats for Trump in 2016, before Biden took them back again in 2020.

Biden is narrowly trailing Trump in the polls this time around, but the annual State of the Union speech gave him a chance to pitch his case for reelection to a national TV audience of millions.

- 'Hyper-partisan' -

Never mentioning Trump by name but referring 13 times to "my predecessor," Biden lashed Trump and the Republicans on everything from abortion to the economy, warning that "freedom and democracy are under attack."

Democrats feted him with chants of "four more years" -- and when Republicans frequently heckled him, especially on the issue of migration, he shot back each time.

Republican House Speaker Mike Johnson, who sat shaking his head in his traditional spot just behind Biden during the speech, said he was not impressed.

"It was a hyper-partisan attack speech," said Johnson, whose party has been dogged by infighting and is currently blocking a bipartisan bill to send military aid to Ukraine.

"Anybody can read a teleprompter... I think he's a very weak president." Biden's speech also took on the war in Gaza, which has provoked fury among leftists and the Arab-American community, angered by Biden's strong support for Israel's attempt to crush Hamas.

He announced that he has ordered the US military to set up a port on Gaza's coast to bring in humanitarian relief, and warned Israel not to use aid as a "bargaining chip."