Former vice president Joe Biden’s sweeping victory in South Carolina turned him into the only viable alternative to Vermont Sen. Bernie Sanders for the Democratic presidential nomination, but there may also be a more subtle force at work in the primaries of Super Tuesday: the coronavirus and the fears it has inspired.

If a majority of Democrats was intent on the question of who can beat President Trump even before the virus’s outbreak, Trump’s partisan, divisive and fact-denying response to the crisis underscored just how dangerous it would be to keep him in office for four more years.

This could push primary voters even harder to consider the question of whom they trust most to wield power in the Oval Office.

Former New York mayor Mike Bloomberg tried to capi­tal­ize on this feeling with an ad in which he talked about the threat of the virus in a setting that made it look as though he was already president. But Biden hopes that he will be the main beneficiary of the public’s uneasiness because it will reinforce his underlying appeal to the value of experience, the virtues of safety and the need to restore stability in governance.

Yet Biden has just days to convert his South Carolina landslide into delegates in the 14 states at stake on Tuesday. And early voting will complicate his task.

Democrats who made their choices before South Carolina did so before the contours of the Biden-Sanders confrontation were defined. This means that former South Bend, Ind., mayor Pete Buttigieg, who left the race Sunday night, as well as Minnesota Sen. Amy Klobuchar and Bloomberg already have votes that might otherwise have shifted to Biden. Massachusetts Sen. Elizabeth Warren also has her share of early votes, although a significant number of her voters might have gone to Sanders rather than Biden.

There is also the tricky math of Democratic Party rules, which could swing scores (and perhaps hundreds) of delegates in California. It awards 144 of its delegates on the basis of the statewide vote and 271 by congressional district. A candidate who receives 15 percent of the votes statewide wins a share of those at-large delegates. A candidate who falls under 15 percent gets none. If only Sanders passes the threshold, he wins all 144 of those statewide delegates.

Polls suggest that Sanders is poised to win a substantial California victory. Biden has hopes now that his South Carolina success may allow him to get over the threshold, which he desperately needs to do. But holding off a Sanders runaway in the biggest state may require at least one more candidate to hit the threshold, too. It’s not clear if any of them can, although the surveys suggest that Warren may be in the best position to do so.

Then there is the Bloomberg Effect. Bloomberg, who has spent hundreds of millions of dollars across Super Tuesday states, could help halt a Sanders delegate pileup by hitting the threshold in states such as Texas, Virginia, Arkansas, Oklahoma and perhaps Tennessee. But Bloomberg’s presence could also stop Biden from winning outright in those states.

A recent Public Policy Polling survey in Texas pointed to Biden’s Bloomberg problem. It offered respondents two scenarios: one with Bloomberg in the race and one without him. With Bloomberg in, Biden was neck-and-neck with Sanders. Without Bloomberg, it showed Biden winning Texas rather handily. But in real life, Bloomberg is on the ballot, and more recent polls suggest Sanders had opened a lead.

Last, Biden will be rooting for Klobuchar to win her home state of Minnesota and Warren to win in Massachusetts. Sanders is strong in both states.

What Biden does have is momentum and endorsements. Without a lot of cash, he is counting on Sen. Tim Kaine (D-Va.) and former governor Terry McAuliffe to push his message across in Virginia. Biden hopes for the same in California from Sen. Dianne Feinstein, former senator Barbara Boxer, former CIA director Leon Panetta and Los Angeles Mayor Eric Garcetti. Sanders will say it’s all a sign of “the Establishment” ganging up on him. It’s a risk Biden is more than happy to take.

But the main effect of South Carolina may be on Biden himself. After a series of primary and caucus losses, the former vice president was looking beleaguered and tired, reinforcing fears among Democrats about his own “electability.” His victory speech on Saturday — focused, moving and strategic — began to ease those doubts.

Biden has a long way to go, and Sanders will always enjoy a big enthusiasm edge. But Biden now has at least some evidence for his case that he is not only the nominee most likely to beat Trump, but also, in an anxious moment, the most plausible president.

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