Canadian-born Ted Cruz has been facing down the backlash of the so-called "birther" movement, as his Canadian birth and former citizenship are raising questions about whether he counts as a “natural-born” citizen, a requirement for presidential office.

The issue was brought up in tonight’s debate, when Cruz was asked about his eligibility for office. He seemed to understand the requirements of American citizenship better than many of his Republican colleagues who previously questioned Obama’s citizenship. “Under long-standing U.S. law, the child of a citizen born abroad is a citizen,” he said.

Cruz is correct: Any child of an American parent is automatically an American citizen, one of the reasons why the questions about Obama’s birth certificate were always fairly meaningless. Despite what he called “some of the more extreme” birther theories, espoused by people — like Donald Trump — that say one must be born on American soil. Trump has been using the fact of Cruz’s birth to suggest that he was disqualified for office.

Cruz took the opportunity to confront the GOP frontrunner on the attacks, and the two bickered back and forth. But Trump was candid about why he was bringing this up now. “Because now he’s doing a little bit better,” he shrugged. Was Trump actually acknowledging a rival?

Nah. “Now he’s probably got a 4-5% chance.”

Cruz was nonplussed. “I’m not taking legal advice from Donald Trump.” Probably a good idea.