Per the New York Times, Rubio was doing what he had planned in the exchange with Christie, although obviously it didn’t come off and the rest is history:
Heading into Saturday night, the campaign’s approach was clear: Mr. Rubio would avoid spats with fellow Republicans and present himself as the candidate best prepared to take on the Democrats in a general election.
That was the idea behind what became the most painful moment of his campaign. In debate preparation sessions, Mr. Rubio had practiced quickly pivoting from skirmishes with Republicans, like Mr. Christie, back to his real target: Mr. Obama and, by implication, Hillary Clinton. And he had made the now infamous point plenty of times before — Mr. Obama wanted to fundamentally change America, by dragging it far to the left, and his success in doing so demonstrated that it was ideology, not experience, that really mattered in a president.
But in the debate, Mr. Rubio’s wording was indirect and confusing, even to his staff. And standing on stage, trading rapid-fire barbs with Mr. Christie, he did not spot the trap that the governor of New Jersey had laid for him by warning the audience of Mr. Rubio’s scripted ways. Every word-for-word repetition of his Obama pivot (“he knows exactly what he’s doing”) sounded like a rattled politician reaching for his security blanket.