Under our Constitution, the federal government has delegated, enumerated and thus limited powers. Power is delegated by the founding generation or through subsequent amendment (that makes it legitimate); enumerated in the constitution (that makes it legal); and limited by that enumeration. As the 10th Amendment says, if a power hasn’t been delegated, the federal government doesn’t have it.
For 150 years, that design held for the most part. When faced with a welfare bill in 1794, for example, James Madison, the principal author of the Constitution, rose in the House to say that he could find no constitutional authority for the bill. A century later, when Congress passed a similar measure, President Cleveland vetoed it as beyond Congress’ authority.
That all changed during the New Deal as both congress and the president sought to expand federal power. When the Supreme court objected, rather than amend the Constitution, Franklin D. Roosevelt tried to pack the court with six additional members. The scheme failed, but the threat worked. Thereafter, the court started reading the Constitution’s General Welfare and Commerce Clauses so broadly that the doctrine of enumerated powers was essentially destroyed — and with it limited government.