How far can Trump go in issuing pardons?

The Constitution gives presidents what appears to be unlimited authority to grant pardons. He “shall have the power,” Article II says, “to grant reprieves and pardons for offenses against the United States, except in cases of impeachment.”

The pardon power extends only to federal crimes. Otherwise, presidents are free to use it as they see fit. As the Supreme Court put it in an 1866 decision involving a former Confederate senator, Ex Parte Garland, the power “is unlimited.”

“It extends,” the court said, “to every offense known to the law.”

In a tweet last year, Mr. Trump indicated that he had studied the matter. “All agree the U.S. president has the complete power to pardon,” he wrote.