A federal pardon in the United States is the action of the President of the United States that completely sets aside the punishment for a federal crime. The authority to take such action is granted to the president by Article II, Section 2, Clause 1 of the U.S. Constitution.
CNN:
The biggest question: will Trump try to pardon himself? We don't know conclusively whether a presidential self-pardon is lawful -- primarily because nobody has ever tried it before. The Constitution places no explicit limitation on the pardon power and legal scholars differ on the issue. ...If Trump does pardon himself, federal courts could eventually give us a definitive answer.
Will Donald Trump attempt to pardon himself?
This resolves positive if, before 21 January 2020, Trump attempts to use the pardon power (under Article II, Section 2, Clause 1 of the constitution) for potential crimes committed by himself. It will resolve positive even if Trump is not charged with any crimes (such as when President Gerald Ford pardoned Nixon, who had not been charged with anything, over any possible crimes connected with the Watergate scandal). It will resolve positive even if courts ultimately rule that the pardon is not legal.