The impeachment process is equally broad, though, and while it must function on a case-by- case basis, it can be used to put guardrails around “essentially unlimited” powers like this. While the Pardon power itself is broad, it is not a license to violate the rest of the Constitution.

Congress can step in and say “Yes, there are limits to the pardon power, because if a President goes too far we can put him in check”, and then define “too far” in the impeachment resolution.