BOSTON — Four years ago, Bernie Sanders won big among white blue-collar voters in the Democratic presidential primary, helping fuel his neck-and-neck run against Hillary Clinton that nearly reached the Democratic national convention.

It also exposed a major vulnerability for Clinton that proved damaging for her in the general election against Donald Trump. 

But this year, as Joe Biden has taken command in the Democratic primary, some of the same demographic groups that didn't back Clinton in 2016 are delivering for the former vice president as he takes on the same opponent. That includes non-college-educated white voters, who could be critical for Democrats to win back the Rust Belt swing states of Michigan, Wisconsin and Pennsylvania. 

Since his breakout win in South Carolina and continuing into his latest romp Tuesday, Biden has vastly outperformed Clinton's 2016 primary performance with two key groups: college-educated voters in affluent suburbs – where there has been a turnout surge – and rural working-class voters. It's why a race many predicted would be a long drawn-out fight is on the verge of collapsing for Sanders, a democratic socialist once considered the front-runner. 

Democrats have reason to be optimistic by voter turnout that's up across the country, particularly in suburbs, which propelled Democrats to control of the House in 2018. And if Biden goes on to the be the nominee, even simply tightening Trump's margins of victory in some areas could spell victory for the Democrats. 

"The party seems far more united. (Biden) seems to be a far less divisive figure than Clinton was," said John Della Volpe, director of polling at the Harvard Institute of Politics. "Clearly, he has some work to do, which is around the youth vote, but the good news I think for him and Democrats is there should be a lengthy opportunity to process what's happened and to reset, repair and rebuild." 

In just a 10-day span, Biden has taken a stranglehold of the nomination fight by coalescing support among Democrats who see him as the best shot to beat Trump and who are motivated to move on to the general election. The broad coalition is led by African American support that matches Clinton's in 2016, but Biden is performing better than Clinton among white voters across the board. 

In Michigan, Biden's inroads on display

Michigan, the top prize of Tuesday's primaries, narrowly went to Sanders four year ago, jump-starting his 2016 surge. But Tuesday, Biden topped Clinton's numbers substantially in every subgroup of white voters, helping him sweep each of the state's 83 counties.

Biden blew out Sanders in Michigan, 53%-36%, despite Sanders pumping major resources into the state – and even though Clinton and Biden are both aligned with establishment politics and ideologically, including their support of NAFTA, a perceived vulnerability in Michigan. In 2016, Sanders won Michigan 50%-48%.

According to CNN exit polls, Biden netted a 24-percentage point swing among white voters over Clinton's performance, spanning both men and women. Sanders beat Clinton with white voters in Michigan56%-42% in 2016. But Biden beat Sanders Tuesday 52%-42%. Biden also netted 20-point gains over Clinton in every sub-group of white Michigan voters: men, women, college-educated and non-college educated.  

"We are learning that some of Bernie Sanders' support in 2016 was more anti-Hillary Clinton support than pro-Sanders support," said Matt Grossman, a political scientist at Michigan State University. "It doesn't seem to have carried over into 2020."

In 2016, Clinton was running to be the first woman president and routinely faced questions of whether the country was ready to elect a woman. She also was seen by some as dishonest, and many found her polarizing. A Quinnipiac University poll this week found 51% of the electorate nationally views Biden honest today, while only 29% said the same about Clinton in August 2016 after she secured the nomination. 

Grossman called the Michigan outcome Tuesday "surprisingly widespread," with Sanders performing better in college towns like East Lansing, but still not as well as 2016. Despite losing black voters overwhelmingly, Sanders actually received slightly better numbers among voters of color in Michigan than four years ago.

"So it really is a white voter loss that is accounting for Sanders doing a lot worse," Grossman said.

He said people shouldn't "over-read" the Michigan results, noting that there's typically no relationship between how a candidate performs in a state in the primary and general election.

"But people in retrospect saw it as a bad sign that Clinton was losing some traditionally Democratic voters that did turn out to be echoed in the general election (for Trump)," Grossman said. "So it's at least a good sign for Biden that he didn't repeat that pattern."

A white working-class comeback for Dems? Don't count on it, experts say

Biden Tuesday pushed his delegate count to more than 850 out of the 1,991 needed to secure the nomination, building his lead over Sanders to more than 150.

Biden clobbered Sanders 60%-35% in Missouri, winning every county again after Sanders came less than 1 percentage point from carrying the state in 2016. Sanders beat Clinton in Washington by a whopping 73%-27% in 2016, but with votes still being counted Wednesday afternoon, Biden and Sanders are in a dead heat. Biden also won Idaho, 49%-43%.

In Mississippi, which has a large African American electorate, Biden nearly matched Clinton in overall support but unlike 2016, Sanders fell below the 15% delegate threshold. Sanders' only projected win Tuesday was in North Dakota, which he also won in 2016.

In all, Biden has won five states where Sanders beat Clinton in 2016: Minnesota, Maine, Oklahoma, Michigan and Idaho. 

Rachel Bitecofer, a political scientist and assistant director of the Wason Center for Public Policy at Christopher Newport University, said the electorate is different than four years ago because turnout is so much greater. That could help explain one reason for Biden's performance. 

Lacking a competitive Republican primary like 2016, independents and Republicans can choose to vote in the Democratic primary in open-primary states like Michigan.

"You also have the sentiment that's driving the electorate now, too," Bitecofer said. "In my research, the electorate was very ideological and nitpicking in 2016, and so it was very anti-establishment and Clinton paid an establishment price. And now the voter pool is really looking toward an establishment candidate as a safety pick, a super risk-averse pick."

But Bitecofer cautioned Democrats from thinking their path to beat Trump is by reversing the loss of white working-class voters who Trump won over. Instead she said it's by continuing gains in suburbs – including in the Rust Belt – and turnout among young voters and voters of color.

"The Democratic victory in 2020 is not going to be on the back of white working-class voters. It's going to be from a turnout surge of Millennial, Gen Z voters and Latinos and African Americans," Bitecofer said. "This idea that Biden's pathway to victory is by reconverting white working-class voters who've been involved in a long-term coalitional realignment away from the Democratic Party is in my opinion a false narrative."

Amy Walter, national editor of the Cook Political Report, tweeted a grim outlook Tuesday night on Democrats' path to winning the Midwest again.

"The story of 2018 was the suburbs," Walter said, referring to Democratic midterm gains in the House. "The ‘comeback’ story for Biden is African-American + suburbs. But, in places like (Wisconsin), suburban vote has not moved as strongly blue and there are still LOTS of small town and rural votes that will be solid red."

Youth vote still lags for Biden

Sanders did not speak publicly Tuesday night after his early losses. But he acknowledged at a Wednesday news conference it "was not a good night" from a delegate standpoint. And while he said his campaign is losing the electability debate, they are winning two others – the ideological and generational debates.

He said he looks forward to debating Biden in Phoenix on Sunday, which takes place two days before primaries in Arizona and three other highly populated states: Florida, Illinois and Ohio.

Biden will be favored in the latter of three, and considerably so in the biggest draw, Florida, where polling suggests he could be positioned to compete for nearly all of the 219 delegates in play.

Nonetheless, one glaring deficiency in the Biden coalition remains young voters, who overwhelmingly back Sanders, albeit not at the turnout rate Sanders has needed. In Michigan, Sanders was the choice of 76% of voters 18 to 29, according to CNN exit polls, compared to 19% support for Biden. Sanders also won voters ages 30 to 44 by a margin of 52%-42%. 

Della Volpe said the Clinton campaign faced a similar weakness with young voters coming out of the primary, and they knew it. But he said the Clinton campaign wrongly assumed young voters would be firmly in her corner with Trump as the Republican nominee.

"What we found is that it was one of the top two or three reasons that she lost," Della Volpe said. "She took them for granted. She didn't get the share of the youth vote that she wanted and they didn't turn out at the number she would have liked.

"So my eyes are going to be looking through that demographic and whether the Biden campaign rebuilds and resets this relationship, because I think there's more that they have in common that unites them than divides them."

Reach Joey Garrison on Twitter @joeygarrison