Any authority and the very existence of Congress is derived form the Constitution. Rand Paul is one of the very few Senators who actually uses the Constitution as a basis for his actions. That is what sets Paul apart, including dealing with the utterly unconstitutional Obamacare, from the rest of the senatorial pack.
I think Paul is bonkers. The choice is not between Graham-Cassidy and a full repeal. The choice is between Graham-Cassidy and Obamacare forever. That is just a fact. If Graham-Cassidy passes, there would still be a chance to repeal or phase it out, etc. If Graham-Cassidy fails we’re stuck with Obamacare forever. (And no, it will never implode. The same Uniparty that can’t repeal it will prop it up indefinitely. Thanks, Paul...for nothing.)