Donald Trump paints possible 2020 rival Joe Biden as 'low I.Q.'

President Donald Trump on Monday gave possible 2020 presidential election rival Joe Biden a taste of what to expect if he does jump in the race, with a tweeted insult about his intelligence.

Biden, who was vice president under Barack Obama and is seen as potentially the most heavyweight Democrat, remains on the sidelines. However on Saturday he appeared to confirm his candidacy before correcting himself in mid-sentence, as if having made a slip of the tongue.

Trump, who delights in inventing mocking nicknames and poking fun at opponents, pounced.

"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!"

Biden's surprise slip -- or, as some speculated, crafty hint -- came during a speech in his home state of Delaware.

"I'm told I get criticized by the new left. I have the most progressive record of anybody running for the United...," he said, immediately correcting himself -- "anybody who would run."