Mr Biden made the comments alongside Michigan Governor Gretchen Whitmer, who was recently found to be the target of a kidnapping plot by a heavily armed right-wing militia.
Joe Biden on Friday described US President Donald Trump's reluctance to denounce white supremacists as "stunning" in a hard-hitting speech in battleground Michigan with 18 days to go until the election.
Standing by the side of the Democratic presidential candidate as he spoke was Governor Gretchen Whitmer, a fierce Trump critic who was recently found to be the target of a well-planned kidnapping plot by a heavily armed right-wing militia.
"Make no mistake, that's who they are, domestic terrorists," Mr Biden told a group of some 20 guests and reporters in the town of Southfield.
"It was the sort of behaviour you might expect from ISIS. It should shock the conscience of every American. Every American. And the failure to condemn these folks is stunning," said Mr Biden.
In a tweet on 8 October as the plot was made public, Mr Trump expressed no sympathy for the governor.
"Rather than say thank you, she calls me a White Supremacist," Mr Trump complained.
"I do not tolerate ANY extreme violence," he insisted.
Mr Trump also infuriated many Americans during the first debate with Mr Biden on 29 September when he declined to denounce white supremacist groups and instead, speaking out to the right wing nationalist group called the Proud Boys, said "stand back and stand by".
The group celebrated its mention by the president by adopting those words as part of a new logo.
Two days later, under pressure to explain himself, Mr Trump said he did in fact condemn all white supremacists.