President Donald Trump told a Pennsylvania crowd Tuesday that he's fighting "Marxists" and "lunatics" while his Democratic challenger Joe Biden accused him in Florida, another key electoral state, of having treated Americans as "expendable" during the Covid-19 pandemic.

With only 21 days until the November 3 election and badly down in the polls, Trump fired every lurid exaggeration about the Democrats and insult about Biden's mental state that he has in his arsenal.

Democratic presidential candidate Joe Biden is to visit Florida to court senior voters
Democratic presidential candidate Joe Biden is to visit Florida to court senior voters AFP / JIM WATSON

He said Biden was "choking like a dog" during their televised debate, called him mentally "shot," and claimed the Democratic frontrunner was the pawn of communists.

"He is handing control to the socialists and Marxists and left-wing extremists," Trump told the large, raucous crowd in Johnstown. "He can't stand up to the lunatics running his party."

Supporters of US President Donald Trump attend a rally at Orlando Sanford International Airport in Sanford, Florida
Supporters of US President Donald Trump attend a rally at Orlando Sanford International Airport in Sanford, Florida AFP / SAUL LOEB

Going even further on his long-running narrative that 77-year-old Biden is too frail for the presidency, Trump, 74, tweeted a crudely faked picture purporting to show Biden in a wheelchair, surrounded by elderly wheelchair-bound people in a room.

"Biden for president," the caption said, with "p" struck out to change the word to "resident."

The mocking presentation of the infirm elderly was somewhat surprising given the president's apparently growing problems in retaining the loyalty of seniors, an important electoral force.

US President Donald Trump at his first campaign rally since his hospitalization for coronavirus
US President Donald Trump at his first campaign rally since his hospitalization for coronavirus AFP / SAUL LOEB
IMAGESIn his first campaign rally since contracting Covid-19, US President Donald Trump takes the stage in Sanford, Florida, himself maskless, and throws red masks out into the audience instead of the usual Make America Great Again baseball caps. Trump ha
IMAGESIn his first campaign rally since contracting Covid-19, US President Donald Trump takes the stage in Sanford, Florida, himself maskless, and throws red masks out into the audience instead of the usual Make America Great Again baseball caps. Trump has repeatedly downplayed the role of masks in containing the virus' spread and was hospitalized with the coronavirus last week. DC POOL

In Johnstown, Trump reprised the outsider image that he developed for his surprise 2016 victory, telling the crowd that he was combating a "selfish and corrupt political class" back in Washington.

But even as he delighted the crowd with his greatest rhetorical hits, Trump once more showed that despite his poor poll showing he has no intention of trying to reach across to Democrats in a deeply divided nation.

"This will end up being a large-scale version of Venezuela if they get in," he said, painting a nightmarish anti-immigrant vision of a country where Democrats give free hospital care to "illegal aliens" while "decimating Medicare and destroying your Social Security."

Charts showing historical voting results in US presidential elections in battleground states, forecasts for 2020
Charts showing historical voting results in US presidential elections in battleground states, forecasts for 2020 AFP / Sophie RAMIS

The coronavirus, which has claimed more than 215,000 lives in America, was largely an afterthought, even if Trump himself was hospitalized for three nights after testing positive at the start of October.

"We're going to crush the virus very quickly. It's happening already," Trump said, despite a swath of the United States now reporting large increases in infections.

Senator Mitt Romney said he was 'troubled' by the rhetoric in the presidential campaign and warned it could lead to a 'very bad place'
Senator Mitt Romney said he was 'troubled' by the rhetoric in the presidential campaign and warned it could lead to a 'very bad place' GETTY IMAGES / ALEX WONG

"Soon it's going to be perfecto," he said.

Supporters look on as Democratic Presidential Candidate Joe Biden speaks during a drive-in rally in Miramar, Florida
Supporters look on as Democratic Presidential Candidate Joe Biden speaks during a drive-in rally in Miramar, Florida AFP / JIM WATSON

Hours earlier, Biden was in Florida holding one of the much smaller events typical of his low-key campaign, zooming in on Trump's handling of the pandemic.

Arguably even more important on election day than Pennsylvania, Florida is a battleground state that Trump won in 2016 but where polls currently show Biden ahead.

Biden courted the elderly, telling an event at a retirement center in Pembroke Pines, north of Miami, that Trump has "never been focused on you."

"His handling of this pandemic has been erratic, just like his presidency has been," he said.

Biden recalled that Trump once remarked that the virus -- which has taken a particularly brutal toll among the elderly -- "infects virtually nobody."

"You are expendable, you are forgettable, you are virtually nobody. That's how he sees this," said Biden, who, unlike Trump, wore a face mask throughout his remarks.

Trump was also in Florida on Monday night for his first rally since recovering from his bout with Covid-19. This week he will be heading out to Iowa and North Carolina, then back to Florida and Georgia.

Iowa and Georgia were two states which Trump won handily in 2016 but polls show tight races in both three weeks ahead of the November 3 election.

And a poll of likely Florida voters released on Tuesday by Florida Atlantic University (FAU) gave Biden a 51 percent to 47 percent lead there.

"Joe Biden continues to be competing better for senior voters than Hillary Clinton did in 2016, and that could be the difference in Florida," said Kevin Wagner, a political science professor at FAU.

Forty-four percent of those polled said Trump's handling of the coronavirus crisis was good or excellent while 50 percent said it was poor or terrible.

Trump has brushed aside the polls, calling them "fake."

According to McDonald's US Elections Project, voters have cast 11.86 million ballots so far in the states that report early voting.