Marco Rubio thought he did well at Saturday's debate. Then he read Twitter.

Whether you think it was a dumb overblown gaffe or a revealing moment that exposed the candidate as a lightweight, Marco Rubio's debate performance on Saturday in which he robotically repeated the same talking point again and again and again (see above) probably contributed to his dismal fifth-place finish in the New Hampshire primary.

Rubio acknowledged this himself, telling supporters during his concession speech Tuesday night, "Our disappointment is not on you, it's on me. I did not do well on Saturday night. But listen to me: That will never happen again."

But he was apparently late to realizing he screwed up. According to a report by the New York Times's Jeremy Peters and Michael Barbaro, Rubio didn't know he had done poorly in the debate until aides told him after, and he didn't get the full extent of the disaster until he checked … Twitter:

The episode was such a shock that not even Mr. Rubio seemed to understand the gravity of the situation as he left the stage at St. Anselm College just after 10 on Saturday night. His wife and four children rushed to greet him in a private back room, followed by somber-faced aides, who delivered their candid assessment.

It was not, Mr. Rubio conceded to them, his best performance. But only after the senator scrolled through Twitter — flooded with brutal, mocking reviews — did he fully grasp the damage he had done to his own campaign.

On the one hand, you can interpret this as a sign of Rubio's self-delusion, that he is so confident of his own abilities that it took him scrolling through every mean thing said about him on social media to realize he'd made a mistake. But that seems unlikely. By all accounts, Rubio is a very anxious person; overconfidence isn't his problem.

The bigger takeaway is that perceptions — and in particular perceptions among journalists, who dominate political Twitter and were likely heavily represented among the feeds Rubio read — matter, and perhaps matter more than the immediate reaction of viewers to a debate. New Hampshire voters didn't just watch the debate, they read three days of brutal media coverage — including here at Vox, including by me — describing it as a big blunder. That almost certainly worsened their view of Rubio, just as it altered Rubio's own opinion of his performance.