Is Presidential Immunity in the Constitution?

Question: Could Congress, consistent with the Constitution, enact a statute making it a crime for any person to direct or participate in the use of American military force in the absence of a declaration of war by Congress against the target of that use of force?

Or how about being more direct in targeting the president: Could Congress make it a crime to issue a pardon to a person who has been convicted of conspiring to defraud the United States?

I think the answer to both these questions is no. The Constitution makes the president the commander-in-chief of the armed forces. The Supreme Court has long held, moreover, that a president is not merely authorized but obliged to use whatever force may be necessary to repel an attack, or even a threatened attack, against the United States. Congress may not use its authority to legislate crimes in a manner that encroaches on the president’s authority to direct military operations. And the Constitution vests the president with the pardon power without qualification. This leads to some sticky questions about bribery (an impeachable offense) — i.e., if the president takes a bribe to issue a pardon, may the president be indicted for bribery even if the pardon (probably) may not be invalidated? But bribery aside, Congress may not constitutionally restrict the president’s pardon power by criminalizing its exercise.