>The U.S. Constitution grants the president pardon power only for federal offenses, not state crimes
This is an imprecise statement. The President may 'grant reprieves and Pardons for offences against the United States'. This is interpreted by some as limiting a President's pardon power to federal offenses but that's not the language the Constitution uses.
Article II, Section 2, Clause 1:
The President shall be Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States; he may require the Opinion, in writing, of the principal Officer in each of the executive Departments, upon any Subject relating to the Duties of their respective Offices, and he shall have Power to grant Reprieves and Pardons for Offences against the United States, except in Cases of Impeachment.
https://constitution.congress.gov/browse/essay/artII-S2-C1-3-1/ALDE_00013316/