Joe Biden has launched one of his fiercest attacks on Donald Trump, branding the presidential hopeful as ignorant, out of touch and unpatriotic.
The US vice-president, looking to exploit what has been a tumultuous week for Mr Trump, slammed the businessman for his comments on Post-Traumatic Stress Disorder, his late night Twitter attack on a former beauty queen, and his tax record.
He told CNN that Mr Trump was "not a bad man" but added: "His ignorance is so profound, so profound".
On allegations that Mr Trump may have avoided paying taxes for nearly two decades, Vice-President Biden said paying taxes is "about making sure you did your part for the country".
"Since when does somebody who lives at the top in the world, in a penthouse overlooking the world, be in a position that he doesn't feel any obligation at all to pay any federal income tax to support the military, to support education, to support our foreign policy?" Mr Biden said.
"Since when is that a patriotic thing to do? Can you imagine any other president, any other president, just ever say that and be proud of that? I can't fathom it."
Mr Biden also accused Mr Trump of being "ignorant" of the sacrifices of military personnel after he caused uproar by suggesting those with PTSD are not strong and "can't handle it".
"How can [Trump] be so out of touch and ask to lead this country?" he said.
Referencing Mr Trump's personal attack on former Miss Universe Alicia Machado, Mr Biden said: "Can you imagine the president getting up at 3:30 in the morning and tweeting vitriol?"
Mr Biden, who opted against running for the White House himself following the death of his son Beau, has thrown his weight behind Hillary Clinton and is currently campaigning for her in the important swing state of Florida ahead of Sunday's second presidential debate.
He believes the former secretary of state would make a "first-rate president".
"I'm working like hell for Hillary. Every time she expresses emotion, she gets clobbered. I know her, I know she cares...[Trump] doesn't deliver anything that's going to change lives."