Speaking at a press conference, Mr Biden said: “He can’t turn the economy around and get America back to work.” Donald Trump’s competitor also said he will name his female running mate next week, in his latest efforts to boost his chances of winning the November election.
Mr Biden joked he would have to avoid TV camera crews so he can meet his new running mate.
Mr Biden said: “I’m going to try to figure out how to trick you all so we can meet in person.
“I’ve got crews outside my house. I don’t think it matters actually.
“What I said is I’m going to have a choice in the first week in August, and I promise I’ll let you know when I do.”
The Democrat gave no hint at who he will pick but previously said he would choose a woman.
Contenders are rumoured to include Senators Kamala Harris, Elizabeth Warren, and Tammy Duckworth.
The former national security adviser Susan Rice, Congresswoman Karen Bass and Val Demings, and Michigan Governor Gretchen Whitmer are also possible contenders.
Mr Biden said he would be one of the “most progressive presidents” in history if elected.
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Mr Biden said: “I think we are going to take back the United States Senate.”
Democrats are confident about their chances in Arizona, Colorado, Maine and North Carolina where the Republican positions appear to be in trouble.
According to the RealClearPolitics average of polls on the presidential race, Mr Biden leads Mr Trump by 9 points.
Mr Biden is also making gains in traditionally red states including Arizona, Texas and Georgia.
This comes as Mr Trump has again defended the use of hydroxychloroquine to fight coronavirus, opposing his own public health officials.
He said the medication, which has been used to treat malaria, is only being rejected as a COVID-19 treatment because he is the one who suggested its use.
Mr Trump said at the White House: “When I recommend something, they like to say ‘don’t use it’.”
There is no evidence the drug can treat coronavirus.
In June, the US Food and Drug Administration (FDA) warned against the use of the drug for COVID-19 after reported said there were “serious heart rhythm problems” and other health issues.
The drug was first mentioned by Mr Trump in March as a treatment for COVID-19.