WASHINGTON — Bernie Sanders lost his make-or-break state of Michigan and Joe Biden delivered big victories that led Democratic elites to confidently declare him their presumptive nominee, marking a dizzying turnaround after the former vice president began the primaries 0-for-3.

Biden won Michigan, Mississippi, Missouri and Idaho, while Sanders prevailed in North Dakota, according to NBC News projections. Washington state, where the candidates were running neck and neck, was still too close to call on Wednesday, but Sanders appeared to be underperforming in most states that voted Tuesday compared to the huge victories he scored in them in his unsuccessful campaign in 2016.

Biden also expanded his already substantial lead in delegates.

Here are five takeaways from a pivotal night in the 2020 election.

1. Sanders' theory of the case fell short. Again.

Sanders' prospects hinged on young progressives' turning out in droves to overwhelm their older moderate-leaning counterparts. That didn't happen on Super Tuesday, and it didn't happen on "Super Tuesday II," either.

The key dividing line in the primary season has been age, with millennials and Gen Z voters overwhelmingly backing Sanders, while older generations flock to Biden.

Meanwhile, Biden's strategy never looked more correct — Twitter isn't real life, the young and online left isn't representative, and Democratic voters are ultimately more pragmatic than ideological. There hasn't been a progressive revolution for change; there has been a suburban revolution for normalcy.

Voters under 30 dipped as a share of the electorate compared to 2016, including in Michigan and Missouri, two key victories for Biden, according to NBC News exit polls. In Livingston County in the Detroit area, one of the wealthiest counties in Michigan, turnout surged from over 17,000 in 2016 to more than 27,000 in 2020. Biden won it by 17 points.

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2. Women are propelling Biden

Women make up a considerable majority of the Democratic electorate, and they're proving to be a key ingredient to Biden's success. He carried them by 33 points in Missouri, by 23 points in Michigan, by 68 points in Mississippi and by 19 points in Washington state. Sanders did far better with men, even winning them in some states.

The gender gap Tuesday comes days after Elizabeth Warren, who is aligned with Sanders on many policy issues, dropped out of the race and raised concerns about the "online bullying and sort of organized nastiness" among some of his supporters. Unlike more moderate candidates — Kamala Harris, Cory Booker, Pete Buttigieg and Amy Klobuchar — who embraced Biden, Warren hasn't yet endorsed.

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3. Black voters are kingmakers

The candidate who has carried African American voters has won every Democratic presidential cycle since 1992, and that streak looks likely to continue in 2020.

Biden's performance among black voters since South Carolina has been nothing short of dominant. They propelled him to a significant delegate lead last week and helped him expand it this week. On Tuesday, he won black voters by 38 points in Michigan, by 48 points in Missouri and by 76 points in Mississippi.

One bright spot for Sanders? He continued to do well among Latino voters after they carried him to victories in states like Nevada and Colorado.

4. Biden is talking like the nominee

"I want to thank Bernie Sanders and his supporters for their tireless energy and their passion. We share a common goal. And together we'll defeat Donald Trump. We'll defeat him together," Biden said in Philadelphia.

In rhetoric and demeanor Tuesday night, Biden seemed like the long-dominant front-runner of 2019 before his campaign took a nosedive in the early states. He evoked the need to unify the country to restore its soul. He warned that America's character was at stake and that four more years of President Donald Trump could permanently alter it.

Democratic groups that had been neutral in the battle are ready to dive in. "The math is now clear. Joe Biden is going to be the Democratic nominee for President and @prioritiesUSA is going to do everything we can to help him defeat Donald Trump in November. I hope others will join us in the fight," said Guy Cecil, the chief of the party's largest super PAC.

5. Team Sanders says he isn't leaving

While Democratic elites are eager to put the primary behind them and shift focus to the general election, top Sanders aides indicated he isn't leaving in a hurry, as he's slated to debate Biden on Sunday in Phoenix.

"The tougher the primary is for the Democratic nominee, the better, more battle-tested the nominee will be," Sanders aide David Sirota tweeted. "Establishment demands for silence in the name of 'unity' — or for the end of a contested primary — don't serve the cause of defeating Trump. They weaken that cause."

Campaign spokeswoman Briahna Joy Gray added: "I, for one, am extremely excited about this debate all the moderates are panicking about...America finally gets to see Biden defend his ideas, or lack there of, on Sunday."