Our official policy is nicknamed "strategic ambiguity" - we do not say what we would do in case of a Chinese attack. We think doing so gives the best chance of preventing an attack.
A MUCH better answer than Biden used to give to that question. The stutter is odd - just took her a minute to remember the policy.
Usually when members of the House get that question - from Gingrich to Pelosi - they screw it up. She got it.