Surely, even for America, this is a questionable part of the Constitution in the modern era? Especially when you see how Trump is now using (abusing?) it.
The plenary power to grant a pardon or a reprieve is granted to the president by Article II, Section 2, Clause 1 of the Constitution; the only limits mentioned in the Constitution are that pardons are limited to federal offenses, and that they cannot affect an impeachment process: "The president shall ... have power to grant reprieves and pardons for offenses against the United States, except in cases of impeachment".
The plenary power to grant a pardon or a reprieve is granted to the president by Article II, Section 2, Clause 1 of the Constitution; the only limits mentioned in the Constitution are that pardons are limited to federal offenses, and that they cannot affect an impeachment process: "The president shall ... have power to grant reprieves and pardons for offenses against the United States, except in cases of impeachment".