US President Donald Trump campaigned frantically and frontrunning challenger Joe Biden stayed mostly out of sight Tuesday ahead of a pivotal televised debate with only two weeks until Election Day.

The contrast in campaign strategies between Trump, 74, and Biden, 77, has never been more pronounced: the Republican president left for another rally in the battleground state of Pennsylvania, while the Democrat played it cool at his home in Delaware -- though he will deploy his former boss, Barack Obama, to Philadelphia for a rally on Wednesday.

Polls show Biden ahead and with the clock running down, he appears confident.

In any case, few could ever out-campaign Trump, who has rediscovered his old energy with daily, sometimes twice-daily rallies around the country since recovering from Covid-19 just over a week ago.

US President Donald Trump
US President Donald Trump believes he's on a roll with two weeks until the election. Photo: AFP / MANDEL NGAN

His latest rally was in Erie, a former Democratic stronghold that he won in 2016, symbolizing his successful capture of the white, working class vote that had long been loyal to the left and which Biden has been trying to claw back.

Trump's message with 14 days to go has boiled down to a mix of optimism, telling Americans that the pandemic is practically over, and ever more extreme attempts to tar Biden as corrupt -- even saying Tuesday that he wants the attorney general to open an investigation ahead of the election.

But, underlining how hard it is for him to escape the subject of the Covid-19 crisis, Trump's wife Melania canceled plans to accompany him to Pennsylvania at the last minute, complaining of ongoing discomfort following her own bout with the virus.

This was to have been her first appearance alongside Trump at a rally in more than a year, possibly boosting his dire standing among women voters.

US President Trump's rally
US President Donald Trump's rallies feature chants of 'lock him up' against opponent Joe Biden. Photo: AFP / OLIVIER TOURON

The trip was canceled due to a "lingering cough" following her infection, a spokeswoman said, raising questions about how well the first lady has really recovered.

After a difficult few weeks for his reelection hopes, compounded by three nights in hospital with the coronavirus, Trump believes he is storming into the final stretch with new momentum -- even if published polls show little sign to support this theory.

Democratic presidential candidate Joe Biden
Democratic presidential candidate Joe Biden is much less visible but leads President Donald Trump in most polls. Photo: AFP / JIM WATSON

"Things are changing fast," Trump told the Fox & Friends program, claiming that his own polling showed Biden is "imploding."

Both candidates will get something of a reality check on Thursday when they meet for their second and final televised debate.

To try and impose some sense of order after a chaotic first clash in September, the moderator will this time switch off the microphone of the candidate not meant to be speaking, thereby trying to thwart interruptions.

In what could be seen as foreshadowing, Trump's microphone cut out briefly at his Erie rally Tuesday. When it came back on, he blamed "Crooked Hillary" for the interruption.

Joe Biden and Donald Trump
Details of the second TV debate between US presidential candidates Donald Trump and Joe Biden on October 22, 2020. Photo: AFP / Alain BOMMENEL

At the debate Biden is sure to go after Trump for his record on the pandemic, which has killed around 220,000 Americans and, despite the president's frequent claims, is surging back rather than going away.

As for Trump, he has made clear his priority is to pursue his murky claim that Biden's son Hunter sold access to his father in Ukraine and China when he was vice president under Barack Obama.

Trump upped his offensive Tuesday by calling on US Attorney General Bill Barr to investigate his "criminal" opponent "before the election."

And he told Fox News that the accusation has sent Biden "into hiding."

Trump is the subject of multiple allegations of sexual assault, corruption, and also is the first president to run for reelection after being impeached.

However, he won in 2016 in part thanks to the success of a last minute push to sow doubt about the honesty of his opponent Hillary Clinton.

He is dusting off that playbook again. Crowds at Trump's rallies have even repurposed the old anti-Clinton chant for Biden, shouting "lock him up."

"The fact is whether you like it or not... Joe Biden is a corrupt politician," Trump told supporters at the rally in Erie on Tuesday.

According to a new poll from The New York Times/Siena College, Biden has a nine-point lead nationally.

Although this reflects the consensus of polls, there are outliers, including IBD/TIPP, which accurately predicted the 2016 shock result and sees a much tighter race now, with Biden only 2.3 points ahead.

Pennsylvania is one of the half-dozen states that Trump more or less has to win to amass enough electoral college votes to hold on to the presidency. Polls show Biden ahead there, though a Reuters/Ipsos poll this week showed the gap narrowing slightly.

Reflecting the state's importance, the Biden team said that Obama would campaign in Pennsylvania on Wednesday at a "drive-in car rally" in Philadelphia during which he will encourage early voting.

Firebrand Senator Bernie Sanders, who is hugely popular with the Democrats' left wing, will go on Saturday.

A key element in this year's campaign is early voting, which is at record high levels amid fears over the spread of the virus. So far, some 34 million Americans have already cast ballots, according to the independent US Elections Project.

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