Joe Biden is the worst candidate in the history of American presidential politics: Donald Trump

US President Donald Trump has described his presidential challenger Joe Biden as "the single worst candidate in the history of America", referring to a few recent gaffes of the Democratic leader.

Republican incumbent Trump, 74, and challenger Biden, 77, are locked in a close contest for the November 3 elections.

"I'm running against the single worst candidate in the history of American presidential politics and you know what that does? That puts more pressure on me. Can you imagine if you lose to a guy like this?" Trump told his supporters in the battleground state of Pennsylvania on Tuesday.

Trump recalled how recently Biden, mid-speech, forgot the name of former Republican presidential candidate Mitt Romney.

"It's unbelievable. It's disgusting. It's disgraceful. If he wins the radical left will be running the country. He won't be running the country. The radical left will takeover. And how about (that), Pennsylvania? So he says there will be no fracking. No fracking!” the president said, as his supporters jeered Biden.

With the elections just 21 days away, Trump exuded confidence of winning the eastern swing state. “And we are going to win four more years in the White House,” he said.

“This election is a simple choice. If Biden wins, China wins. All these other countries win. We get ripped off by everybody. If we win, you win, Pennsylvania wins, and America wins. Very simple,” he said.

“For years the selfish and corrupt political class betrayed the people of Pennsylvania. You know that. And the people of our country. Career politicians like Joe Biden lied to you,” the president said.

He criticised Biden for his views on migrants and troop deployment in the Mid-east.

"Biden's a servant of the radical globalists, the wealthy donors, the big money special interest who shipped away your jobs, shut down your factories and you know it. Because you really suffered right in this area. Threw open your borders and ravaged our cities while sacrificing American blood (soldiers) and treasure in these ridiculous, endless foreign wars. They're (soldiers) all coming back home. Don't worry. They're all coming back home. Soon. They're already on their way," Trump said. 

(Image: AP)