The concept of "what the constitution SPECIFICALLY authorizes the government to do" was debated by the founders and for the two hundred years since its adoption - original intent vs living document.
Rep. Paul is obviously of the Scalia, Bork "original intent" belief. I dont suggest they are necessarily wrong...
...But there are
equally compelling and valid arguments for the "living document" school of thought as expressed by Thurgood Marshall (among many other jurists and judicial scholars)
"The Constitution must be interpreted in light of the moral, political, and cultural climate of the age of interpretation."