Time Magazine called this the “your mama” response in presidential political debates. Since the entire eligibility issue for Ted Cruz hinges on his mother’s status as a natural-born citizen of the US (thereby making him one despite his birth in Canada), Cruz’ pushback against Trump seems appropriate — if a bit of a reach. Cruz obviously prepared for this moment, and delivered his attack with considerable flair and relish:

https://www.youtube.com/watch?v=yu7LckmS70o

Trump, the bombastic billionaire, remains atop the polls nationally but locked in a tight race with Cruz in Iowa. That’s why Trump has been shivving Cruz on his constitutional eligibility, even though most legal scholars consider this another sideshow. Cruz was ready with a rejoinder questioning Trump’s own qualifications.

“At the end of the day, the legal issue is quite straightforward,” Cruz said calmly. He had prepared for this moment. After all, he didn’t win national debating championships by happenstance. “But I would note that the birther theories that Donald has been relying on, some of the more extreme ones insist that you must not only be born on U.S. soil, but have two parents born on U.S. soil. Under that theory, not only would I be disqualified, Marco Rubio would be disqualified, Bobby Jindal would be disqualified and, interestingly enough, Donald J. Trump would be disqualified.”

The moment caught Trump by surprise. “Not me!”

Oh, yes, you. A woman born in 1912, in some voters’ minds, might be the thing that finally disqualifies frontrunner Trump from the most powerful office in the land

“Donald’s mother was born in Scotland. She was naturalized,” Cruz continued with the calm of a former Supreme Court lawyer, which he is.

“But I was born here. Big difference,” Trump said, trying to set this attack back on track and stretching out the adjective as long as he could. “Big” became a very big word. He knew the clip was going to be a cable news favorite.

“On the issue of citizenship, Donald, I’m not going to use the issue of your mother’s birth against you,” Cruz said. It was a fantastic reminder that no white paper, no policy address can compete in the modern era of political campaigns with the snide dagger stabbed just below a rival’s rib cage.

Watch the clip all the way through to see Cruz’ level of preparation. Trump tries to respond to Cruz’ ridicule of Trump and this issue by bringing up Laurence Tribe as his expert, a move which is known as a fallacy of authority: Trump isn’t making his own legal argument, but simply citing Tribe as an authority. Cruz springs the trap by explaining Tribe’s political affiliation and his support for Hillary Clinton. Cruz practically licked his chops waiting for Trump to slip on that banana peel.

Will this make any difference at all? Eh … doubtful. According to observers who might normally not want to credit Trump, he had a very good night otherwise. Cruz and Marco Rubio reportedly had excellent nights, too. At this stage, the candidates are probably too well adapted to the format — and voters too familiar with the candidates — to expect any real game-changers from the debates. But those who want to see strategy, preparation, and delivery might find themselves more impressed with Cruz.