<p><br />LAS VEGAS — A naughty moment from Hillary Clinton? A waggish, impish moment? And during a debate yet?</p><p> Standing onstage for two hours can test the mettle of the presidential candidates. And it also tests their kidneys. Which is why, when CNN cut away for commercials Tuesday night, the candidates rushed offstage and headed for the bathrooms.</p><p> But Hillary barely made it back on time after one break.</p><p> “Secretary Clinton, welcome back,” CNN moderator Anderson Cooper said.