Last Sunday, I argued that despite his stagnation in the polls, for Republicans (and non-Republicans) who would prefer that Donald Trump not be renominated for the presidency, Gov. Ron DeSantis of Florida remains pretty much the only possible alternative.

Naturally the week that followed was the worst yet for DeSantis, beginning with a campaign staff purge that featured a Nazi-symbol subplot and ending with the candidate doing damage control for his suggestion that Robert F. Kennedy Jr. might run his Food and Drug Administration.

The worst news for DeSantis, though, was new polls out of Iowa showing Senator Tim Scott of South Carolina creeping up on him, with around 10 percent support, to the governor’s roughly 15 percent.

One of my arguments a week ago was that no other Republican, Scott included, had yet shown any capacity to build the support that even a stagnant DeSantis enjoys. But if the governor falls into a sustained battle for second place, he’s probably finished, and Trump can probably just cruise.

Unless that battle results in a DeSantis collapse and a chance for someone else to go up against the front-runner. After all, why should DeSantis be the only non-Trump hope just because he seemed potent early on? Why not, well, Tim Scott?

Say this for Scott: He has an obvious asset that DeSantis is missing, a fundamental good cheer that Americans favor in their presidents. Say this as well: He has the profile of a potent general-election candidate, an African American and youthful-seeming generic Republican to set against Joe Biden’s senescence. Say this, finally: Scott sits in the sweet spot for the Republican donor class, as a George W. Bush-style conservative untouched by the rabble-rousing and edgelord memes of Trump-era populism.

But all of these strengths are connected to primary-campaign weaknesses. To beat Trump, you eventually need around half the Republican electorate to vote for you (depending on the wrinkles of delegate allocation). And there’s no indication that half of Republican primary voters want to return to pre-2016 conservatism, that they would favor a generic-Republican alternative to Trump’s crush-your-enemies style or that they especially value winsomeness and optimism, as opposed to a style suited to a pessimistic mood.

The reason that DeSantis seemed like the best hope against Trump was a record and persona that seemed to meet Republican voters where they are. His success was built after Trump’s election, on issues that mattered to current G.O.P. voters, not those of 30 years ago. He could claim to be better at the pugilistic style than Trump — with more to show for his battles substantively and more political success as well. On certain issues, Covid policy especially, he could claim to represent the views of Trump’s supporters better than Trump himself. And with DeSantis’s war on Disney, nobody would confuse him for a creature of the donor class.

All this set up a plausible strategy for pulling some Trump voters to DeSantis’s side by casting himself as the fulfiller of Trump’s promise — more competent, more politically able, bolder, younger and better suited to the times.

This strategy was working five months ago, and now it’s failing. But its failure doesn’t reveal an alternative pitch, and certainly Scott doesn’t appear to have one. Indeed, as The Bulwark’s Jonathan Last points out, Scott isn’t really casting himself as a Trump alternative; he’s mostly been “positioning himself as an attractive running mate for Trump, should the Almighty not intervene” and remove the former president from the race.

So for him to surpass DeSantis and become Trump’s main adversary could be what Last describes as a “catastrophic success.” It might lead to a weird sacrificial-lamb campaign, in which Scott contents himself with the quarter of the primary electorate that currently supports him in head-to-head polling against Trump. Or it could push him to come up with a pitch to be Trump’s successor. But it’s hard to see what would make that pitch stronger than the one that isn’t currently working for DeSantis.

After all, the governor has a substantial record of policy victories; Scott has rather fewer. DeSantis has been successful in a contested political environment; Scott is a safe-seat senator. DeSantis was arguably as important a Republican as Trump during the crucial months of the Covid era; Scott was insignificant. DeSantis has struggled to expand his policy pitch beyond Covid and anti-wokeness; Scott doesn’t even have that kind of base to build on.

For DeSantis to defeat Trump would make sense in light of the G.O.P. landscape as we know it. For Scott to win would require a total re-evaluation of what we think we know about Republicans today.

Such re-evaluations happen, or else Trump himself wouldn’t have been president. Success creates unexpected conditions; if Scott surpasses DeSantis, he will have the chance to make the most of them.

But for now, his climb in the polls looks like a modest victory for his own campaign and a bigger one for Trump’s.