After Donald Trump’s win in South Carolina on Saturday, there seemed to be a general consensus about where the Republican race stood, one we pretty much agreed with. Trump, according to betting markets, had about a 50 percent chance of becoming the nominee. Marco Rubio, who had closed strongly to finish in second place in South Carolina, had about a 40 percent chance as the leading traditional candidate. And the rest of the GOP field had only about a 10 percent chance combined.

But somehow over the course of five days between the South Carolina primary and the GOP debate in Houston on Thursday night, the conventional wisdom changed. The news media began to talk about Trump as not just the plurality favorite, or the odds-on frontrunner, but instead as the “inevitable” Republican nominee. Trump’s stock shot up in prediction markets to a 75 percent chance of the nomination.

Was this justified or out of proportion? Certainly, Trump had a good week. He crushed his competition in Nevada. He got excellent polls in states such as Florida and Virginia. He earned his first two endorsements from members of Congress. And some reporting suggested that major GOP donors were unwilling to contribute to anti-Trump advertisements, even though Trump could be a total disaster for the Republican “establishment.”

Some of these achievements are not quite the unambiguous successes they might seem, however. Trump’s Nevada win was yuge, as you might say, but fairly close to what was predicted by polls and prognosticators, meaning that the result could have been priced into the conventional wisdom beforehand. Meanwhile, with so many polls coming out in so many states, it can be easy to cherry-pick: Trump had a really excellent set of polls on Thursday, but he had some mediocre ones earlier in the week. Those endorsements? Yes, Trump finally got on the board, but Rubio got 20 of them since South Carolina while also knocking Jeb Bush out of the race.

Then Rubio took matters into his own hands in the Houston debate. I’d written ahead of time that it would be smart for Rubio to attack Trump, so you won’t be surprised to learn that I thought he had a good night, even though Trump was effective in parrying some of the attempts. My FiveThirtyEight colleagues agreed — Rubio averaged an A- in the grades our staff submitted anonymously, as compared to a B for Ted Cruz and a C+ for Trump.

CANDIDATE AVERAGE GRADE HIGH GRADE LOW GRADE Marco Rubio A- A+ B- Ted Cruz B A D Donald Trump C+ B+ D- John Kasich C A- F Ben Carson D+ A- F FiveThirtyEight’s Republican debate grades

Will voters at home see things the same way? There’s always the chance they won’t. Furthermore, there’s reason to think that most of Trump’s supporters are firmly attached to him: Even if Trump has a ceiling, he also has a floor, with 30 percent to 35 percent of Republican voters having been committed to him for months.

Even if Rubio doesn’t pick off many Trump supporters, however, his debate performance probably helped him in other respects. First, while it can be easy to overestimate how much this matters, he’ll probably succeed in changing his news coverage a bit. The media, perhaps having grown wary of Rubio’s previous overpromising, had been taking an increasingly glass-half-empty view of his candidacy. Even though Rubio had some decent news this week — the endorsements, the Bush dropout, a series of polls showing him pulling ahead of Ted Cruz in Southern states, a couple of second-place finishes — the press wasn’t having any of it. Now, at the very least, they’ll need to introduce some notes of caution, while Rubio will improve the morale of his supporters and surrogates.

Second and more importantly, Rubio emerged forcefully as the anti-Trump candidate. In contrast to his previous, sometimes passive performances, Rubio was so eager to be the alpha male on stage that he’d butt in on exchanges between Trump and Cruz in addition to picking his own fights with Trump. That sends a signal to Republican voters, donors and party elites: If you want to take down Trump, I’m your guy. These Republicans can now choose to coordinate around Rubio as an anti-Trump focal point, both in the sense of having the best chance to beat Trump and as the best conduit for attacks.

The debate could also inspire further attacks on Trump from Rubio and other Republicans. Lines of attack on Trump University or Trump’s employment of undocumented immigrants haven’t been tested much, but that’s better for Rubio than their having been tested and failed.

Rubio does have a narrow path to the nomination. It will probably require, first, for him to improve upon his current polling on Super Tuesday: Even a couple of percentage points taken from Cruz would probably be enough for Rubio to beat Cruz almost everywhere but Texas. A couple more percentage points and Rubio could be competitive with Trump in states like Virginia. Then he’ll have to make some further progress before March 15, when winner-take-all Florida and Ohio vote, and probably hope that one or more of his rivals drops out. Polls of a hypothetical one-on-one matchup between Trump and Rubio show a competitive race.

It’s not a great hand to play, particularly since there’s no guarantee Rubio’s rivals will concede the race any time soon. But we’re already so far off the empirical radar in terms of anything that has happened in a nomination campaign that it’s hard to assess the odds exactly. Perhaps that’s why prediction markets have fluctuated so much: Trump at once seems like the inevitable GOP nominee and an impossible one. In Houston, Rubio put that existential dilemma aside and recognized that, whatever Trump’s odds to begin with, they’ll be lower once he’s finally attacked.

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