As the special counsel investigation into Russian interference in the 2016 election continues to close in on President Donald Trump and his closest advisors, there have been reinvigorated concerns that he will attempt to use his pardon power to undermine the investigation.

While concerns about the lengths to which Trump will go to protect himself and his inner circle from accountability are well-founded, there are important limits to the pardon power. The president’s pardon power cannot be used to: (1) pardon state crimes, (2) remove federal civil liability, (3) pardon impeachment, or (4) pardon crimes that have not already occurred.