What is an example of the constitution denying absolute or arbitrary power on the government?

Article I, Section 9, sets limits on the government. Article II, Section 2 both grants and limits the president's appointment powers. For example, the president may make treaties as longas two-thirds of the Senate concurs. Amendments 9 and 10 are also examples of the limitations placed on the federal government by the U.S. Constitution.

The Supremacy Clause, or Article VI, Clause 2, establishes the U.S. Constitution as "the supreme law of the land". So you know that this document does indeed have authority.