One question has dominated this year’s crowded, confusing Democratic presidential primary:

Which one of these people has the best chance of defeating President Trump?

Just days ago, it seemed as if Democrats might never settle on an answer. There were six major candidates still in the race. Joe Biden had yet to win a contest. Mike Bloomberg loomed large. Bernie Sanders was the tentative frontrunner.

But Biden’s 28-point victory in South Carolina on Saturday triggered one of the most rapid turnarounds in recent political history, and by the time the dust settled on Super Tuesday, Biden had swept Southern states that had been toss-ups as recently as last weekend (North Carolina, Virginia) and Northern states that had looked like locks for his rivals (Massachusetts, Minnesota).

Biden won Texas, a state where Sanders led in eight of the last nine polls, and looked likely to hold Sanders to a single-digit margin of victory in California, a state where Sanders had hoped to amass an insurmountable delegate lead.

All of a sudden, Biden seemed to have the clearer path to the nomination — and to beating Trump. That’s because the results on Super Tuesday — the closest thing to a national primary in American politics — validated the former vice president’s claim to electability and undermined his rival’s.

Joe Biden addresses a primary election night campaign rally on Super Tuesday, March 3, in Los Angeles, with his wife, Jill, left, and his sister Valerie. (Chris Carlson/AP)

Of all the 2020 candidates, the two septuagenarians have always offered the starkest contrast on the issue of what it will take to oust Trump. Sanders has long said he will win by adding votes on the left. Biden claims he will win by holding onto voters in the middle.

At his Super Tuesday night rally in Burlington, Vt., Sanders vowed that his candidacy would “create the highest voter turnout in American political history” — particularly among young voters, new voters and voters of color. It’s one of his signature lines, a cornerstone of his “political revolution.”

Yet Sanders has not demonstrated that he can deliver on this promise. In every one of the 15 states and territories that voted Tuesday, Sanders drew a smaller share of the vote than he drew during his primary contest against Hillary Clinton four years earlier. Even in his home state of Vermont, he won only 52 percent of the vote, down from 86 percent in 2016.

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In the run-up to Super Tuesday, a New York Times analysis found that the demographic groups Sanders is counting on have not been turning out in historic numbers, either. The Times reported that in the Iowa precincts where Sanders won, turnout increased by only one percentage point from 2016; that turnout increased far more in the New Hampshire townships won by former South Bend, Ind. Mayor Pete Buttigieg and Minnesota Sen. Amy Klobuchar, than those where Sanders won; that the share of young voters remained essentially unchanged everywhere; and that the share of first-time voters actually decreased.

Those patterns largely persisted on Super Tuesday. According to the exit polls, the youth turnout was down from 2016 in Alabama, North Carolina, Tennessee, Virginia, Vermont and Texas — and in many cases, Sanders won a smaller share of the youth vote than he did last time around.

“If you’re Bernie Sanders, this is your worst-case scenario,” commentator Van Jones said on CNN. “Because you’re now beginning to see the logic of the revolution begin to break down — the idea that you’re going to have young people come out in large numbers.”

Sen. Bernie Sanders of Vermont meets supporters at a campaign rally in Springfield, Va. on Feb. 29, 2020. (Susan Walsh/AP)

(A new study by political scientists at Yale and the University of California, Berkeley, showed that nominating Sanders would drive many Americans who would otherwise vote for a moderate Democrat to vote for Trump — losses that Sanders could only offset by inspiring an unprecedented 11-percentage-point turnout boost among young left-leaning voters.)

Biden mocked Sanders’s rhetoric during his own election night rally in Los Angeles. “People are talking about a revolution,” Biden said, referring to Sanders. “We started a movement. We’ve increased turnout. The turnout turned out for us!”

Biden was correct to claim that his core supporters had shown up — particularly in suburban swing districts across Virginia, North Carolina and even Texas, which are likely to play a major role in Democratic efforts to defeat Trump’s GOP in November.

In Virginia, 1.3 million Democrats voted, nearly double the 722,000 Democrats who voted in the 2016 primary, and also far ahead of turnout in 2008, which was 976,000. Biden won the state overwhelmingly, with 53 percent of the vote to Sanders’s 23 percent.

“It doesn't seem great for Sanders’s electability narrative that turnout seems to be increasing more in states where he isn’t doing as well,” said analyst Nate Silver, founder of the data journalism site FiveThirtyEight.

In Fairfax County, Va. — the dense suburban county just outside Washington, D.C. — Biden received almost 129,000 votes, compared to the 88,000 votes Hillary Clinton received there in the 2016 primary.

Neera Tanden, the president of the Center for American Progress, a liberal think tank, said that Democrats should remember the 2018 midterms, when they regained control of the House of Representatives largely by flipping Republican seats in suburban districts.

“The suburban tsunami was how we won then,” Tanden tweeted. “We ignore these lessons at our peril for 2020.”

Former Obama White House press secretary Robert Gibbs agreed. “Suburban neighborhoods … are crucial in a swing state in a general election,” Gibbs said on MSNBC. “Those are the places where the congressional candidates took seats from Republicans in 2018 and where somebody’s going to have to do well in 2020 to be next president of the United States.”

Then there was the African-American vote. Biden trounced Sanders among black voters, a bedrock Democratic constituency. In North Carolina, Biden beat Sanders by 40 points among African-Americans. In Virginia, Biden’s margin was even larger: 55 points.

Super Tuesday may have been disappointing for Sanders, but with wins in Colorado, Utah and Vermont, plus a likely victory in delegate-rich California, he will remain close to Biden in the overall delegate count. That is in large part because of his impressive Latino outreach program, which propelled him to victory in the Nevada caucuses and helped him outpace Biden by 34 points among Latinos in California.

Yet even there — a state where Sanders opened 23 field offices — the Latino share of the electorate was down two percentage points from 2008, according to preliminary exit polls. In Texas, it was unchanged from 2008 and 2016.

While it's impossible to say for sure which Democratic candidate would perform best in a general election, Super Tuesday showed that Biden can turn out the voters he needs to compete. Sanders, meanwhile, has yet to prove that he can lure his coalition to the polls in record numbers.

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