MIAMI (AFP) - President Barack Obama cut loose with a barn-burner campaign appearance Thursday (Nov 3), energising tepid Florida Democrats to get out, vote and give Hillary Clinton the chance to take up his mantle.

Leveraging every ounce of his high approval ratings, Obama deployed the same oratorical flair that brought him into the White House in support of a would-be successor he once described as "likable enough."

In turns coaxing and berating - leaning on the podium and banging his fists - Obama tried to inject energy and optimism into the nasty, bruising race between Donald Trump and his Democratic rival.

Two years of shrill campaigning have only added to America's disdain for politics and politicians.

Obama tried to turn that alienation on its head, saying his achievements in office were actually theirs.

"It's because of you that 20 million people have health insurance that didn't have it," he said. "It's because of you that we made this progress."

"I'm not just asking you to believe in Hillary's ability to change things. I'm asking you to believe in your ability to change things."

"Hillary Clinton will move us forward if you give her a chance."

Obama was caustic and dismissive of Trump, who the president is shadowing across Florida on Thursday.

"Anybody who is upset about a Saturday Night Live skit, you don't want in charge of nuclear weapons. I'm serious," Obama said.

"This is a guy who tweets they should cancel Saturday Night Live, 'I don't like how Alec Baldwin's imitating me.' Really?

"This isn't a joke. This isn't Survivor. This isn't The Bachelorette. This counts."

Speaking at a rival rally moments later, Trump hit back, questioning why Obama was wasting time outside the Oval Office when he won't be there for long.

"Why isn't he back in the White House bringing our jobs back? And helping our veterans? Why?" he told supporters.