WASHINGTON — President Trump has consulted his legal advisers about the possibility of pre-emptively pardoning his associates — and possibly even himself — to undermine the Justice Department’s Russia investigation, The Washington Post reported Thursday night. But on Friday, John Dowd, Mr. Trump’s new personal lawyer, denied to BuzzFeed that any such discussions had taken place.

Either way, the chatter has heightened interest in several key legal issues about the scope and limits of Mr. Trump’s clemency powers. Here is what you need to know:

What is the pardon power?

The Constitution gives the president clemency powers “to grant reprieves and pardons for offenses against the United States, except in cases of impeachment.” By bestowing a pardon on someone who committed a federal crime, the president nullifies the legal consequences of that crime.

May a president issue prospective pardons?

Yes. In Ex parte Garland, an 1866 case involving a former Confederate senator who had been pardoned by President Andrew Johnson, the Supreme Court made clear that the pardon power “extends to every offense known to the law, and may be exercised at any time after its commission, either before legal proceedings are taken or during their pendency, or after conviction and judgment.”

It is unusual for a president to issue a prospective pardon before charges are filed, let alone a conviction proving that someone committed a crime, but there are examples. In 1974, after President Richard M. Nixon resigned to avoid being impeached in the Watergate scandal, President Gerald R. Ford shut down the possibility that his predecessor might be indicted by issuing “a full, free and absolute pardon” to Mr. Nixon for all federal crimes he “committed or may have committed” during his presidency.