O'BRIEN: What do you make of what he's saying? Of these 23 executive actions, are there some that you think would be targets for being struck down by a court?

KAINE: There's the completely anti-government wing that will make that argument. I guess they made it against President Bush 41 when he by executive action banned the importation of certain kinds of assault weapons. They made it with respect to an executive order signed by President Clinton.

Presidents have the power to do executive orders. That's a power that's conferred on the president by Congress and by the constitution. So there are those -- as Rand Paul says, he wants to nullify. Nullification is a code word.