The one silver lining in Joe Biden's weaker-than-expected performances in Iowa and New Hampshire was that they gave him the chance for a "comeback" in South Carolina, where he retained a potential reservoir of support among the black and moderate white voters who dominate the state's Democratic electorate. Biden's advantage was temporarily shaken—several polls after New Hampshire showed his lead in South Carolina narrowing to single digits—but a combination of his second place finish in Nevada last Saturday, sharper-than-usual debate performance on Tuesday, and key endorsement from veteran congressman Jim Clyburn, the House Majority Whip, on Wednesday helped propel him to a victory of nearly 30 points.
It's likely that Biden will benefit from a few days of very positive media coverage heading into Super Tuesday, and that a number of elected Democrats will rally around him as the most viable remaining alternative to Bernie Sanders. But Biden still has a ways to go before he reclaims his position as front-runner in the race. Sanders will probably win a decisive victory in California on Tuesday, where much of the vote has already been cast by mail and is thus insensitive to a Biden surge, that may alone provide him with a significant lead in the national delegate count. It's also unclear what proportion of any last-minute decline in support for Warren, Buttigieg, or Bloomberg will migrate to Biden, and how much will be transferred to Sanders instead.
It does seem as if the Democratic contest is quickly heading toward a showdown between Sanders and Biden, though polls suggest that Bloomberg is poised to accumulate a chunk of delegates on Super Tuesday that could conceivably matter to the final outcome. (A two-candidate race would provide some clarity to the question of whether there will be a contested convention, since one or the other will have a majority of delegates.) But can Biden, who suffers from a much smaller war chest and weaker campaign organization than one would expect a two-term vice president to have, actually keep up with Sanders once the election calendar accelerates from Tuesday onward? The answer to that question may well hold the key to the nomination.