The first big spat of Saturday night’s debate was between Chris Christie and Marco Rubio, or rather from Chris Christie towards Marco Rubio. Rubio was asked about his experience, specifically what his accomplishments were in the Senate; he answered with a riff explaining that "Joe Biden" was experienced and Obama was bad. Christie pressed the point, saying directly that Rubio "does not have the experience" to be president.
After a rote Rubio reply, Christie did what Chris Christie does best: be a jerk. He mocked Rubio for a "memorized 25 second speech" rather than answering the question, telling him the Senate "does not prepare you" for the presidency. Rubio then began to repeat the exact same mini-speech; Christie called him on it again.
The exchange ended with a rattled Rubio and a clearly satisfied Chris Christie. It's not clear whether Christie did himself any favors with the hostile change, but it definitely hurt Marco Rubio.