POTUS: I'm pardoning everybody in your state who has a drug conviction.
STATE GOV: No, you aren't.
POTUS: You have to let all of those people out of prison.
STATE GOV: No, we don't.
POTUS: It's an emergency!
STATE GOV: No, it isn't.
Did the Federal Government send in the military to enforce the federal 55 mph speed limit? No, your state would just get cut off from federal funding (funding for which, BTW, came from the state’s citizens to begin with).
So, don’t let ‘em out? Have fun funding the housing of the pardoned with your own state’s dollars. Is it worth that much to you, Governor It-is-the-principle-not-the-money?
This is exactly the answer. It's also the reason for perennial disputes about states rights, and the exact reason that the constitution was written the way it was - all rights not specifically enumerated lie with the states. Unfortunately, the interstate commerce clause has become the mother of all loopholes, and the federal government has ballooned to be an order of magnitude (at least) larger than it was ever intended to be. And now it wields all this unintended power and collects copious amounts of tax revenue, which it then turns around and wields against the states to exercise yet more power.
The federal speed limit is a law passed by Congress. We're talking about executive action here, and the President is specifically forbidden by law to impound funds without Congressional authorization.
I suppose the idea is that the "pardoned" prisoners would sue their states demanding release. If the Supreme Court bothered granting cert it would be to write the shortest, nastiest 9-0 "absolutely not" opinion ever.
What next? Send in the army?