A few weeks after Romney’s loss in late 2012, I went to a Dolphins game in Miami with Rubio. At the time it was clear that the senator had big plans, and was increasingly viewed as a leading G.O.P. presidential prospect. He was billed on the cover of Time as “The Republican Savior.” Rubio was refusing most interviews, but I convinced him to talk to me on the condition that we would discuss only football, with which he is obsessed. (His wife is a former Dolphins cheerleader.) My story ran in the sports section, which was a career highlight for both of us.

At only one point did I violate our ground rules, and flagrantly. “So, are you running for president?” I asked Rubio before a key third-down play in the second half. “Not today,” Rubio said. It was unclear whether he was objecting to my question, or answering it in a particularly literal way.

But Rubio was quite clearly laying the groundwork for a campaign. As he had throughout his political career in Florida, he was deftly working his angles, keeping up appearances as a young conservative insurgent while forging alliances across the proverbial establishment; he had no interest in becoming toxic to his colleagues in the Senate, as Ted Cruz had become. By late 2014, it seemed apparent that Rubio’s biggest foe might be his home-state icon and onetime mentor, Jeb Bush. It feels like a million years ago that the two of them were playing Establishment Chess with each other, trying to wall off the other from key donors, endorsements and staff hires. Rubio managed to triumph over Bush against not insignificant odds, for as much as that’s worth now.

On the night before the New Hampshire primary, I caught Rubio in the midst of a rough patch. It was two days after a humiliating debate performance in which he repeated the same bit over and over again as if stuck in a hellish loop of Talking Point Muzak. He kept going on about how it was time to “dispel once and for all that Barack Obama doesn’t know what he’s doing” because, in fact, Obama “knows exactly what he is doing.” The president, Rubio said (and said), is engaged in a “systematic effort to change America.”

In what was easily the pinnacle of Chris Christie’s soon-to-expire campaign, the New Jersey governor taunted Rubio for relying on “memorized 30-second speeches,” while Rubio, looking slightly wild-eyed, countered by attempting to bury everyone in yet more memorized 30-second speeches. Christie would drop out three days later, but his critique of Rubio — that he was a robotic lightweight, “the boy in the bubble” — resonated.

We were riding on Rubio’s campaign bus through a snowstorm en route to a rally in Nashua, N.H. Rubio was tired, as everyone was, but he also seemed slightly dazed. As we approached the event site, he looked out the window and noted the hazardous roads. He wondered aloud whether they should have canceled the event: “Remember what happened to Ben Carson?” A few weeks earlier, a car accident on an icy road in Iowa had killed a Carson campaign worker and injured three volunteers.

Rubio should have stopped there, but he didn’t. “The last thing we need is a story that somebody died on the road,” he added. It was a rare moment of exhaustion transparency that showed just how deeply the grim calculus of the campaign news cycle had seeped into the candidate. His chief concern was the “optics” of someone dying on the way to one of his events. It would be bad “story” for the campaign. (Rubio added later that it would be a “tragedy” if there was an accident.)