Saturday’s debate showed very clearly that the other “establishment” candidates competing with Rubio in New Hampshire don’t buy into the theory that they should step aside for the good of the party. On the contrary, Christie went out of his way to damage Rubio, and Kasich and Bush were more than happy to benefit from that. None of them accepts that Rubio is the default or obvious choice, and one reason for that seems to be that they’re all in agreement that he isn’t remotely prepared for the presidency when compared with any of them. Following the debate, none of them is thinking about how or when to bow out to clear the way for Rubio. They are all interested only in beating him, and at least one of them is likely to succeed this week.
In Christie’s case, it is mostly a matter of payback. Rubio’s allies put up very effective attack ads targeting him in New Hampshire and stomped out whatever flickering embers of hope his campaign might have had, and now he is returning the favor as best he can. It’s also possible that Christie genuinely doesn’t think Rubio is qualified to be president, and therefore he sees the attempt to “anoint”  him as the alternative to Trump and Cruz as a serious mistake. Bush’s determination to take Rubio down also seems to be primarily motivated by anger against Rubio’s perceived betrayal, but his disdain for Rubio’s lack of achievements in the Senate also seems real. If Rubio really were as “manifestly superior”  to them as his boosters claim, they might not be able to justify continuing their campaigns just to settle a score, but they don’t accept that he is.
The refusal of the governors to give up and play along with Rubio’s bad campaign strategy shouldn’t be surprising. While many pundits and reporters assume Rubio is a more viable contender for the nomination than they are, the governors naturally believe differently. Despite the fact that the three governors’ overall unfavorability ratings within the party really are terrible (all of them have 2-to-1 negative ratings), they are viewed favorably by the third of the party that is divided up among them. Those are the Republicans that matter for the “establishment” candidates in the short run. Another common assumption is that Rubio is simply a more competent candidate than Kasich or Bush, but as the last debate showed that is not necessarily true.
Once Walker dropped out, Rubio inherited the dubious role of being the “consensus” candidate who supposedly has the ability to unify all factions of the party behind him. This is a role that Rubio has been embracing as part of his broader electability argument. The trouble with being in that position is that there usually isn’t a lot of enthusiasm for such a candidate. The “consensus” candidate is touted as such mainly because he is unobjectionable to most of the party. As a result, he gets stuck trying to please different factions of the party at the same time during the primaries and ends up satisfying only a few. When he gets in trouble, he has relatively few loyal supporters that are genuinely for him rather than just being against everyone else.
Because Rubio is so obviously the favorite of Republicans in Washington and New York, he is perceived to be part of the so-called party “establishment,” but the reluctance of many party leaders and donors to get behind him deprives him of most of the tangible benefits of that association while loading him down with a lot of extra baggage. Being stuck in the “middle lane”  that Walker tried and failed to occupy, Rubio tries to combine alarmist rhetoric to compete with the demagogues while hewing to his scripted lines on policy to placate party elites. That produces the absurd robotic anti-Obama talk we heard Saturday.
Instead of making him the party’s unifying leader, this makes him seem unreliable to people on all sides of the party. As James Poulos points out  in his review of the debate, it is a lack of trust in Rubio that holds him back:
His lousy performance on Saturday could change the whole race. This isn’t a partisan spin thing. Established Republicans and Democrats, devoted conservatives and liberals, all began lining up behind the story. Why? Because so few people really trust Rubio.
His “establishment” rivals haven’t been in any hurry to exit the race in part because they assume that Rubio wouldn’t be a reliable standard-bearer for the party. His rivals see him as untrustworthy, and so they are understandably unwilling to entrust the fortunes of the party to him. The fact that they are doing this even though it almost certainly ensures a Trump or Cruz nomination shows just how little faith the governors have in the senator.