I'm still waiting for that one as well... Surprised he hasn't even tried the lame "but... but GENERAL WELFARE!!!!" argument yet...
Don't be naive, a lot of things aren't specified in the Constitution, i.e., Executive Action, Executive Privilege, formation of Air Force, military draft, number of Justices on SCOTUS, paper money, Federal Reserve, political parties, primary elections, etc., etc., etc..
The Commerce Clause, Article I Section 8, Judicial Review, 14th Amendememt, plus an array of other vehicles make the Constitution a living document, it is not locked in the 18th Century, even Jefferson admitted that he wasn't a strict constructionist