For Trump, as we were just discussing, it's whether his opinion about a judge of Mexican ancestry makes him a racist.
For Clinton, it's whether or not she is prepared to recognize that the Second Amendment guarantees a real right.
Clinton's answer was apparently to reject the idea, adding that if hypothetically it did she would still be free to regulate it. Well, not just her: she thinks that this hypothetical Constitutional right should be subject to regulation by every level of government: the Federal government, yes, but also "states and localities." Not that she admits that there is such a right.