So did Nixon's Justice Department.
https://www.washingtonpost.com/opinions/no-trump-cant-pardon-himself-the-constitution-tells-us-so/2017/07/21/f3445d74-6e49-11e7-b9e2-2056e768a7e5_story.html?utm_term=.9e728350cd26
Laurence H. Tribe is the Carl M. Loeb University Professor and Professor of Constitutional Law at Harvard Law School. Richard Painter, a law professor at the University of Minnesota, was chief White House ethics lawyer for President George W. Bush from 2005 to 2007 and is vice-chair of Citizens for Responsibility and Ethics in Washington (CREW). Norman Eisen, a senior fellow at the Brookings Institution, was chief White House ethics lawyer for President Barack Obama from 2009 to 2011 and is chair of CREW.
Can a president pardon himself? Four days before Richard Nixon resigned, his own Justice Departments Office of Legal Counsel opined no, citing the fundamental rule that no one may be a judge in his own case. We agree.
The Justice Department was right that guidance could be found in the enduring principles that no one can be both the judge and the defendant in the same matter, and that no one is above the law.
The Constitution specifically bars the president from using the pardon power to prevent his own impeachment and removal. It adds that any official removed through impeachment remains fully subject to criminal prosecution. That provision would make no sense if the president could pardon himself.
SNIP