President Trump on Tuesday cornered Democratic challenger Joseph R. Biden about his son, Hunter, getting rich off foreign deals while his father was in the White House.

Mr. Trump asked Mr. Biden why his son pocketed more than $3.5 million from the wife of Moscow’s mayor.

“What did he do to deserve it?” demanded Mr. Trump at his first debate with Mr. Biden in the 2020 presidential race.

Mr. Biden responded that it was “totally discredited,” referring to the longtime allegations of conflicts of interest and sweetheart deals for his son in countries where Mr. Biden spearheaded Obama administration policy.

Mr. Trump kept pressing him: “What did he do for it?”

Mr. Biden repeatedly said, “It’s not true.”

The former vice president said that wasn’t what the American people wanted to hear about.

“It doesn’t want this. It wants to talk about you, the American people, that’s what we should talk about,” Mr. Biden said.

Hunter Biden has long been under suspicion for cashing in on his father’s clout as vice president in the Obama White House and pocketing millions of dollars in sweetheart deals in China, Ukraine and Russia.

As a result, the younger Mr. Biden has loomed large in the presidential race, though left-leaning news media mostly avoids the subject.

He was at the center of House Democrats’ impeachment of Mr. Trump this year. The abuse of power charges against Mr. Trump stemmed from his pressuring Ukraine to investigate alleged corruption involving Hunter Biden’s lucrative business deals while his father led Obama administration efforts in that graft-riddled country.

Everywhere the elder Mr. Biden went, Hunter Biden seemed to cash in on mega deals, despite limited business experience and a history of drug addiction.

Joseph Biden and Hunter Biden have denied any wrongdoing.

A Senate Republican report last week