1) The GOP has never threatened to shut down the government to defund Obamacare. In fact, they've been quite clear that they will fund everything but Obamacare.
2) The GOP will never leverage the debt ceiling into defunding Obamacare. Why? Because it involves using wise political negotation skills and they don't have the political will do to what is right.
This is indeed a turning point for the GOP. They need to either stand up for real principles, or just throw in the towel and admit they got nuthin.