Mike Konczal suggests Paul's commitment to federalism kneecaps his ability to take on mass imprisonment:

When researchers run statistics over state-level incarceration rates, they find things like "controlling for social disorganization, religious fundamentalism, political conservatism, and violent crimes, the results show that Republican strength [in state governments]…lead to higher imprisonment rates. Statistical interactions support predictions that these relationships became stronger after greater Republican stress on law and order."  States with a Republican governor and Republican legislatures show a greater increase in incarcerated populations, and that the effect is stronger in the 1990s.  Institutions like ALEC were most effective at the state level in changing laws to bias towards longer sentencing.  State laws are crucial to understanding the massive run-up in mass incarceration, and that is where much of the battle will be.

There’s a lot to be done at the federal level, but any serious critique of mass incarceration needs to tackle the states, and the federal level will need to play a part in it.

Damon Root thinks the "state rights" position is, in some ways, fundamentally unlibertarian.