Chris Christie may not be doing well with voters, but he just made a huge point in debate.
Rubio doesn’t actually talk and debate; he just recites and rearranges “modules” of argument or anecdote. This can give the impression of being spontaneous if you have a lot of different modules memorized, and if you use them well. But it’s a shortcut.
This is a pretty standard technique in certain religious apologetics circles.
Since Marco Rubio is the guy who became Mormon and then talked his whole family into becoming Mormons, and then became Catholic again and talked his whole family into becoming Catholics again, I think we can assume that he studied apologetics at some point (and probably had it used on him in the first place). So this is not surprising, but it is a weakness if you rely on one particular technique to do all your work.