President Biden and ex-leader Trump push Pennsylvania Senate candidates ahead of midterms on November 8, an election Biden says marks a "defining" moment for US democracy.

"Democracy is literally on the ballot. This is a defining moment for the nation and we all, we all must speak with one voice," Biden says. (AFP)

President Joe Biden, Democratic superstar Barack Obama and Republican firebrand Donald Trump have all converged on Pennsylvania to push their parties to the finishing line in a race Biden said marks a "defining" moment for US democracy.

Speaking to thousands in a cheering Philadelphia arena on Saturday, Biden said voters face "a choice between two vastly different visions of America."

Biden and the Democratic candidates labeled the Republicans as the party of the wealthy and emphasized their own support for trade unions, social security and reinforced protections for rights to abortion.

But Biden, citing Trump Republicans' growing support for conspiracy theories undermining elections, said an even bigger agenda was at stake.

"Democracy is literally on the ballot. This is a defining moment for the nation and we all, we all must speak with one voice," Biden said.

The battle of the serving and two former presidents on marked the start of a final crescendo before Tuesday when Americans will decide who controls Congress during the last two years of Biden's first term.

READ MORE:Biden 'optimistic' about midterms as Trump signals 2024 comeback

Republicans winning in polls

Polls put Republicans well ahead in the fight for the House of Representatives and also show them with momentum in the Senate as voters, already riled up by culture wars, seek to take out frustration over four-decades-high inflation and rising illegal immigration.

With Pennsylvania one of the handful of swing states that will decide the overall balance of power, both sides brought out maximum firepower.

Biden and Obama rallied in Philadelphia alongside Senate candidate John Fetterman and governor candidate Josh Shapiro.

Before joining the Philadelphia rally, Obama appeared in Pittsburgh to tear into Republicans as a party that wants to "gut" social security and "give rich folks and big corporations more tax cuts."

Still the party's most bankable star six years after leaving the White House, Obama hopes his support will tip the balance for Fetterman.

READ MORE: Biden, Trump launch multi-state campaigns as midterms near

Trump's comeback bid

Trump, who was defeated by Biden in 2020 but has spent the interval promoting conspiracy theories and plotting his own possible White House comeback, held a rally in Latrobe alongside Fetterman's opponent, TV celebrity doctor Mehmet Oz, and Shapiro's far-right opponent Doug Mastriano.

Trump called for a Republican "giant red wave" to defeat Democrats in next week's midterm elections.

"If you want to stop the destruction of our country and save the 'American Dream,' then this Tuesday you must vote Republican in a giant red wave," he told a rally in the crucial state of Pennsylvania, referring to the party's traditional colour.

Just a few kilometres east of Pittsburgh in Latrobe, Trump sought to firm up support in a region that delivered him big margins in the 2016 and 2020 presidential elections.

Success for candidates he supports on Tuesday would help Trump launch his own comeback campaign, despite facing serious legal threats over attempts to overturn his 2020 defeat and the hoarding of top secret documents from the White House at his Florida golf resort.

Pennsylvania is seen as a must-win for control of the Senate, but it also weighs on the balance of power among the country's 50 state governors, whose decisions impact most aspects of voters' lives, from education and health care to voting rights.

Democratic gubernatorial nominee Shapiro has been spotlighting the fringe views of Mastriano and his involvement in the Trump-led attempt to overturn the last election.

A victory for Trump-backed Mastriano would give the prominent election denier oversight of the state's voting system for the 2024 presidential race.

Trump, 76, has already claimed baselessly that the state's elections have been "rigged," echoing his false claims that his own 2020 defeat was the result of fraud.

"As Biden's approval rating plummets, Pennsylvania crime spikes, and Pennsylvanians grapple with a 74 percent hike in heating oil, coupled with record inflation, just weeks away from winter," Trump's office said in a statement.

"The America First Movement offers the Keystone State an alternative vision for America: safe streets, cheap gas, low inflation, and a thriving American economy."

READ MORE: Biden implores voters to save democracy from lies of 'MAGA Republicans'

Source: AFP