The president can grant amnesty for a crime that has not yet been charged or convicted, although it doesn't happen often.
Giuliani's hunt for dirt was part of the Trump administration's shadow foreign policy channel with respect to Ukraine, a top-down effort which included the president himself trying to strongarm the Ukrainian government into launching politically motivated investigations against the Bidens to help Trump's reelection bid. But in recent weeks the idea of preemptive pardons has returned to the Trump orbit, this time including allies and members of his family.
There were no immediate details of the crimes for which Mr. Giuliani allegedly wanted a pardon.
But sources say Trump has not to this point embraced the idea of preemptive pardons, with some aides concerned that a preemptive pardon could be seen as an admission of guilt of some kind.
"Not true at all", he told the Daily News in a text message.
CNN also reported this month that in recent weeks, Federal Bureau of Investigation agents in NY have gotten in touch with witnesses to ask about the former NY mayor's work in Ukraine as well as any possible links to Russian intelligence.
The most famous example of a blanket pardon before indictment occurred when Gerald Ford pardoned Richard Nixon after the latter resigned. George Washington pardoned plotters of the Whiskey Rebellion, shielding them from treason prosecutions.
"It might be unseemly, might be a conflict of interest, but I don't know that it would be unconstitutional", said Louis Seidman, a professor at Georgetown who clerked for U.S. Supreme Court Justice Thurgood Marshall.
Trump pardoned Michael Flynn, his former national security adviser, last week. One witness we know of got beaten up and is in the hospital.