Mr Trump was not completely cleared by former Special Counsel Robert S Mueller III on questions of obstructing justice by trying to interfere with the Justice Department's Russia election meddling investigation. And it appears Mr Trump was repeatedly referred to as "Individual 1" for having knowledge of or possibly committing crimes in documents crafted by federal prosecutors in the case of Michael Cohen, the president's personal lawyer who was sentenced to prison on federal charges.

Should any possible charges come from those, or other, matters, Mr Biden said late Thursday he would not issue a pardon for Mr Trump.

"It is not something the president is entitled to do, to direct a prosecution or decide to drop a case. It's a dereliction of duty," Mr Biden told MSNBC.

"It's hands off, completely," the presumptive Democratic presidential nominee said, referring to any federal probes of MR Trump. "The attorney general is not the president's lawyer. It's the people's lawyer. We never saw anything like the prostitution of that office like we see it today."

That means Mr Biden would not follow an example set by Gerald Ford. The 38th president pardoned former President Richard Nixon in 1974 after the 37th president became the lone American chief executive to ever step down.

But one big difference: Mr Ford had been Mr Nixon's hand-picked VP. Another: Both were Republicans.

Mr Trump was impeached by the House -- and later cleared by the GOP-run Senate -- on charges he abused his power in dealings with Ukraine and obstructed a congressional probe. But neither constitute crimes.

Some legal experts have suggested any possible post-presidency legal trouble for Mr Trump would emanate from the federal prosecutors in the power Southern District of New York.

The president's businesses remain based in New York state, though he has moved his permanent residence to Florida.

Mr Trump has been fairly prolific with the presidency's pardon powers. Most recently, he has not ruled out one for Michael Flynn, the retired Army three-star general and his first national security adviser. The president fired Mr Flynn, saying he lied to the FBI and Vice President Mike Pence about his communications with a senior Russian official.

But the president has defended Mr Flynn in the three years since that firing, and expressed vindication when the Justice Department dropped all charges. The Obama administration started the probe of Mr Flynn that led to his firing and the federal charges, and Mr Trump has made the matter a central theme of his "Obamagate" conspiracy theory that Barack Obama and Mr Biden were at the center of a plot to take down his 2016 White House bid then hobble his presidency.

Mr Biden has denied knowing anything about a criminal probe into Mr Flynn. Mr Obama appeared to respond with a Thursday tweet that simply said: "Vote."