Last week, Donald Trump announced that he plans to pardon figures including Martha Stewart and Dinesh D’Souza—inspiring a conversation about presidential pardoning power. Can the president pardon anyone he likes? Does anything keep that power in check? If the president himself were under investigation for, let’s say, obstruction of justice, would it be possible for him to pardon himself?

A 20-page letter drawn up by Trump’s legal team and confidentially sent to Robert Mueller earlier this year alleges that he can—and that the president has the power to “terminate an investigation at any time for any reason.” On a Sunday morning segment of This Week with ABC’s George Stephanopoulos, Trump’s personal attorney, Rudy Giuliani, sat down to parse the contents of this letter. And while Giuliani said that he doesn’t think Trump would either pardon himself or terminate the Mueller investigation, based on our country’s constitution, he probably could if he wanted to.

That said, Giuliani acknowledged, the optics of a president pardoning himself for obstruction of justice would be tough for the American people to bear. “I think the political ramifications of that would be tough,” Giuliani said. “Pardoning other people is one thing. Pardoning yourself is another. Other presidents have pardoned people in circumstances like this, both in their administration and sometimes the next president even of a different party will come along and pardon.”

The January 29 letter drawn up by Trump’s legal team also argues that it would be impossible to indict or subpoena Trump or any president, due to the president’s position as “chief law enforcement officer”—another supposition that has proved controversial.

“It remains our position that the President’s actions here, by virtue of his position as the chief law enforcement officer, could neither constitutionally nor legally constitute obstruction because that would amount to him obstructing himself, and that he could if he wished, terminate the inquiry, or even exercise his power to pardon if he so desired,” reads the letter, first reported on by The New York Times.