Joe Biden has finally done it. After 32 years and three separate bids to become the Democratic Party’s standard bearer, Biden has at long last won a presidential primary. Nor was his victory one that can be waved aside. After dismal showings in Iowa (where he finished fourth), New Hampshire (where he finished fifth), and Nevada (where he finished a distant second), Biden was genuinely triumphant in South Carolina. Biden led the popular vote with 48.4 percent, far ahead of Bernie Sanders at 19.9 percent. Scores for each of the remaining candidates fell under the crucial 15 percent threshold needed to collect delegates.

Biden’s victory was powered by his strong support among African Americans (61 percent versus 17 percent for Sanders). But beyond that, Biden won among almost all other categories, including white voters (33 percent to Sanders’s 23 percent). The only major demographic that Sanders did well with was young voters under 30 (Sanders received 43 percent, as against 26 percent for Biden). One reason Sanders did so poorly in South Carolina was that people under 45 were only 29 percent of the electorate, as against 37 percent in Nevada.

Biden’s victory in South Carolina was no mere happenstance. His campaign invested heavily in the state, even at the expense of allowing other contests to suffer. As The New York Times reports, “In the last week, Mr. Biden essentially bunkered down in South Carolina to achieve his campaign-saving victory, while Mr. Sanders has been building up his operation, airing ads and making inroads across the country.”

The strategy seems to be that a massive victory in South Carolina will allow Biden to take command on the eve of Super Tuesday and become the chief moderate alternative to Bernie Sanders.

MSNBC host Joe Scarborough argued, “This is a big win for Biden. As he’s been saying for months, Biden can win primaries that look like the Democratic Party. Most other candidates cannot. The race is reset.” (Just as a factual matter, it wrong to say South Carolina looks more like the Democratic Party than other states already contested. According to FiveThirtyEight, Nevada is the fifth most representative state in terms of resembling the Democratic Party, while South Carolina ranks 46th.)

For the South Carolina gamble to pay off, Biden will need a big bump on Super Tuesday. In one crucial respect, Biden has already collected on his bet. Two of his rivals, Tom Steyer and Pete Buttigieg, have dropped out of the race. The race is getting closer to the two-candidate contest between him and Sanders that Biden clearly wants.

In some ways, the narrowing of the campaign is ambiguous. According to a recent Morning Consult poll, the second-choice picks for Buttigieg voters are Sanders (21 percent), Warren (19 percent), Biden (19 percent), and Bloomberg (17 percent). If Buttigieg’s support did distribute itself like this, it would mostly be a wash for Sanders in terms of the electoral results.

Where the dispersal of Buttigieg support might make a difference, however, is in the delegate count. Warren, Bloomberg, and Biden are all under the 15 percent threshold in some Super Tuesday states. Picking up erstwhile Buttigieg voters could boost them above that hurdle and cost Sanders delegate seats.

As FiveThirtyEight notes,

Buttigieg was projected to get under 15 percent in the vast majority of states and districts on Super Tuesday. Thus, his votes were essentially wasted. Redistributing his votes to other candidates will help them to meet the 15 percent threshold, however. In particular, Sen. Elizabeth Warren and former New York Mayor Michael Bloomberg were both close to the 15 percent line in many states or districts. So even an extra percentage point or two would help them get over that line in more places. For instance, both Bloomberg and Warren were projected to finish with an average of 14 percent of the vote in California before Buttigieg’s dropout. Now, they’re forecasted for 16 percent instead.

The narrowing of the race, at least at this juncture, increases the chances of a brokered convention where no candidate has more than a plurality of delegates. But beyond the delegate math, which is still speculative given uncertainty of how Super Tuesday will play out, the political logic of Buttigieg’s quitting the race supports Biden, since it helps consolidate the anti-Sanders vote.

In his speech announcing that he was ending his candidacy, Buttigieg took a few potshots at Sanders without mentioning his name. “We need leadership to heal a divided nation, not drive us further apart,” Buttigieg said. “We need a broad-based agenda to truly deliver for the American people, not one that gets lost in ideology. We need an approach strong enough not only to win the White House, but hold the House, win the Senate and send Mitch McConnell into retirement.” This is an implicit endorsement of the moderate argument that Sanders is too extreme to win and would cost the Democrats congressional seats.

NBC news reports that the Buttigieg campaign has reached out to the Biden campaign to consider “potentially coordinating or teaming up their support.”

An alliance of the moderate candidates behind Biden is probably the best way to stop Bernie Sanders from becoming the nominee. The question is whether that alliance is coming too late in the day. Millions of early votes have already been cast in Super Tuesday states.

Elizabeth Warren, Michael Bloomberg, and Amy Klobuchar remain in the race. They are all likely to eat into Biden’s support. And if there is a brokered convention, it’s by no means certain that Warren’s delegates, if they were free, would go to Biden. Joe Biden risked everything on South Carolina. His victory there is impressive. What remains in doubt is whether it’ll have the large ripple effect he needs to secure the nomination.