Sen. Cory Booker Cory Anthony BookerThe movement to reform animal agriculture has reached a tipping point Watchdog confirms State Dept. canceled award for journalist who criticized Trump 3 reasons why Biden is misreading the politics of court packing MORE (D-N.J.) called it "so offensive" that former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE had to defend himself on Tuesday night's debate stage against President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE's allegations that he participated in corruption in Ukraine.

Booker criticized how the second topic covered in the Ohio debate was Biden, and his son Hunter Biden's business dealings in Ukraine during the Obama administration.

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"We are literally using Donald Trump's lies, and the second issue we cover on this stage is elevating a lie and attacking a statesman," Booker said.

He added that the former vice president "should not have to defend" himself.

"The only person sitting at home enjoying that was Donald Trump seeing that we're distracted from his malfeasance and then selling out of his office," Booker said.

Cory Booker: "We are seeing all over this country, women's reproductive rights under attack … women should not be the only ones taking up this cause and this fight" #DemDebate pic.twitter.com/LrweuacqXU — CNN Politics (@CNNPolitics) October 15, 2019

The Democratic presidential debate, the fourth so far, is the first since House Democrats launched an impeachment inquiry into Trump following a whistleblower report that focused on Trump's July 25 phone call with the Ukrainian president in which he pressed his counterpart to look into Biden and his son.

Hunter Biden served on the board of a Ukrainian gas company that was investigated by a Ukrainian prosecutor who Biden pushed to remove due to the prosecutor's handling of corruption in the country.

Trump and Republicans have engaged in a sustained campaign focused on Hunter Biden's involvement with foreign businesses to accuse him of profiting off his father's office and paint the former vice president as corrupt.

Hunter Biden told ABC News in an interview Tuesday that he regrets taking actions that allowed for attacks against his father.

"I gave a hook to some very unethical people to act in illegal ways to try to do some harm to my father. That's where I made the mistake," Hunter Biden told ABC News. "So I take full responsibility for that. Did I do anything improper? No, not in any way. Not in any way whatsoever."