Anything and everything anytime
It’s one of the more unusual challenges in this most unusual of all US election campaigns.
Republican presidential candidate Donald Trump said at a rally on Tuesday he was ready to fight Vice President Joe Biden behind “the barn”.
And he labelled Mr Biden “Mr Tough Guy” at the Florida event.
For his part, Mr Biden suggested he would like to fight Mr Trump “behind the gym” amid the furore over the Republican’s attitude to women.
That was on Friday. Two days later Mr Biden rowed back a little.
But both men have a history of rough-and-tumble altercations as teenagers so who would win if it got physical?
The Washington Post reported that Mr Trump was sent away to a military school as a teenager to correct his behavioural problems and bullying. Neighbourhood kids were warned to stay away from Mr Trump because he was known for beating them up.
By his own admission, little has changed. He once told a biographer: “When I look at myself in the first grade and I look at myself now, I’m basically the same.”
Mr Trump has proven his toughness, in business deals and on the sidelines. Once he bet on a wrestling match with the head of World Wrestling Entertainment (WWE), Vince McMahon.
In a staged event, when Mr McMahon’s wrestler lost in the ring Mr Trump put Mr McMahon in a headlock and shaved his head.
On Tuesday Mr Trump told his supporters: “Did you see where Biden wants to take me behind a barn? Me. He wants it. I’d love that.”
In a profile of the vice president, the New York Times said Mr Biden was a popular kid as a teenager with a good punch. He was a star athlete on his high school American football team and in college.
In 2015, Mr Biden appeared in a video doing bicep curls for campaign on healthy living called #GimmeFive started by Michelle Obama. Mr Biden appears in the video at his desk, curling a 30lb (13.6kg) weight, and says “I do a million of these a day – just give me five”.
At Friday’s rally in Pennsylvania Mr Biden said: “The press always asks me, don’t I wish I was debating him? No, I wish we were in high school and I could take him behind the gym. That’s what I wish.”