Gloves off as Biden eyes Trump knockout in 2020

But could the bravado belie how much the president in fact fears the prospect of going toe-to-toe with his fellow septuagenarian, who leads him handily in early polls and threatens to poach his base?

Make no mistake: in the months to come, sparks will fly as the New York business tycoon who won the 2016 election without any political or diplomatic experience trades blows with the old Beltway hand and lion of the Democratic party, who first entered the US Senate in 1973.

If at first glance there is plenty that separates the two men, they also share much in common.

Both style themselves as ardent defenders of the working classes, court voters in Middle America, and, in their own very different ways, are known for their plain-speaking.

"Because of his blue-collar strength in states Trump won in 2016, Biden is a real threat to Trump," said Larry Sabato, a political scientist at the University of Virginia.

But to get there, Biden needs to beat a crowded field vying for the Democratic nomination, "and he’s never done well in presidential primaries," added Sabato.

During the 2016 campaign, then once more in 2018, the former Democratic senator had expressed in his own inimitable fashion and, one suspects, only half in jest, his desire to physically thrash the Republican billionaire over his attitude toward women.

"They asked me would I like to debate this gentleman, and I said no. I said, 'If we were in high school, I'd take him behind the gym and beat the hell out of him,'" Biden told an audience at the University of Miami last year.

It didn't take long for a reply. "Crazy Joe Biden is trying to act like a tough guy," tweeted Trump, who called his opponent "weak, both mentally and physically," and added: "he would go down fast and hard, crying all the way."

Julian Zelizer, a professor at Princeton University, told AFP: "In some ways, Biden offers the best chance for Trump to unleash his firepower with someone who will be seen as comparable opponent," predicting no holds barred confrontations between the pair.

- Pale, male and stale? -

"Joe Biden got tongue tied over the weekend when he was unable to properly deliver a very simple line about his decision to run for President," Trump tweeted. "Get used to it, another low I.Q. individual!"

And when Barack Obama's second-in-command found himself coming under fire over his unsolicited physical contact with multiple women, Trump was quick to troll his rival's video apology with his own doctored clip that showed a fake Biden creeping up on the real version and placing his hands on his shoulders.

"WELCOME BACK JOE!" Trump wrote above the video.

Many Democrats denounced the intervention as unacceptable, coming as it did by a man accused by more than a dozen women of sexual misconduct -- and who declared in a notorious 2005 recording that leaked during the 2016 campaign that being a star allowed him to grab women "by the pussy."

He later put the remarks down to "locker room talk."

Trump meanwhile has attacked Biden as part of the political old guard that is out of touch and has nothing new to offer the country.

Presidential advisor Kellyanne Conway got her own jabs in this week, deriding Biden and Bernie Sanders, the independent socialist Senator currently polling second in the Democratic race, as "old white male career politicians" -- a dig referencing the fact that their party has positioned itself as the voice of women and minorities.