Amendment XXVIII
Section 1. The President may be prosecuted for any act not expressly authorized by law.
Section 2. The authority of the President to grant reprieves and pardons shall not extend to himself or any accomplice.
2/
"But no pardon may issue for any offense occurring during a person's term of office where they hold any office whatsoever of trust or honor under the United States or of any State, or for the president, vice-president, or any direct relation of the same, except as Congress may provide by law"
No roadblock for investigations clause: No holding of immunity is allowed to affect eligibility of evidence if the president or any associate (read: accomplice) are in violation of criminal law