Now you're sounding like Alan Dershowitz.
A president's power is not absolute. He does not have the power to obstruct justice.
Had he not resigned, Richard Nixon -- you may have heard of him -- faced certain impeachment and probable conviction for ordering the CIA to tell the acting FBI director to stop an investigation into money laundering through Mexico by Nixon's re-election campaign.
A president cannot order an investigation into his actions be stopped, and not pay a price.