WASHINGTON, DC, USA (AFP) — US President Donald Trump on Thursday deployed his trademark blend of crude humour and Twitter to mock potential election rival Joe Biden’s apology for having touched women without permission.

Biden, an undeclared frontrunner for the Democratic nomination to take on Trump in 2020, had earlier tweeted a short video in which he promised to respect “personal space” more in the future.

Trump responded by posting a doctored version of the video in which a fake image of Biden creeps up behind the actual Biden and puts his hands on his shoulders.

“WELCOME BACK JOE!” Trump writes above the video.

The joking tweet is in keeping with Trump’s long history of mocking opponents with sexual innuendo, schoolyard-style nicknames, and torrents of tweets.

If Trump’s stunt was meant to bait Biden into a back and forth, it succeeded.

“I see that you are on the job and presidential, as always,” Biden clapped back at Trump on Twitter.

In September 2017, eight months into his term, Trump retweeted a video splicing footage of him hitting a golf ball and former 2016 presidential opponent Hillary Clinton falling over, so that it seemed she had been knocked down by his ball.

Biden, 76, defended himself over instances where he kissed women on the head or put hands on them, suggesting he was merely affectionate and politics is about “making connections”.

But in the video he said he would be “more mindful about respecting personal space in the future”.

Biden has not declared officially but polls show the former vice president under Barack Obama and long-time senator would be a formidable challenger to Trump.

Trump faces a litany of far more serious allegations about his behaviour around women — including multiple affairs, and claims of rape, groping and harassment that he has dismissed.

Just before the 2016 election a decade-old recording was released in which Trump could be heard boasting about “grabbing” women’s genitals.

Trump said that he was “not proud” of his words but that they were just “locker room talk”.

Biden’s retort suggests that, should the Delaware Democrat enter the presidential fray, he just might be prepared to get into the mud with The Donald.

Had he been in school when he heard Trump’s misogynist comments, “I’d…beat the hell out of him,” Biden told Florida students last year.