Former Vice President Joe Biden, riding a wave of momentum from primaries in South Carolina and Super Tuesday states, comes into Tuesday’s Michigan primary with a 24-point lead over Sen. Bernie Sanders in a new Detroit Free Press poll.

If Biden’s 51%-27% lead in the poll, done by EPIC-MRA for the Free Press and its media partners, holds, it would guarantee him a signature victory in Michigan – a battleground state that helped President Donald Trump win the White House four years ago. It could also starve Sanders' formerly front-running campaign of delegates needed for the nomination and call into question how long his effort can remain viable.

"Something happened on Super Tuesday with (other) candidates getting out and people are all of a sudden questioning Bernie’s positions on issues," said Bernie Porn, pollster for Lansing-based EPIC-MRA, which conducted the survey of 400 likely Democratic primary voters between Wednesday and Friday. "If anything, it may be low in terms of the percentage that Biden may get."

On Monday, Monmouth University also released a poll of Michigan showing Biden up 51%-36% on Sanders. And a CNN/SSRS poll released Monday showed leading Sanders 52%-36%. Taken together, they strongly suggest Biden has a clear advantage on Sanders ahead of Tuesday's vote.

There is reason for caution among supporters of both candidates, however.

Four years ago, the Free Press and EPIC-MRA reported results of a poll the weekend ahead of that year’s Democratic primary that showed Hillary Clinton with a 25-point lead on Sanders, the independent senator from Vermont. It was one of several polls that showed the former secretary of state with such a lead.

Sanders went on to win a narrow 1.4-percentage-point victory in the primary, however, as younger voters, who overwhelmingly supported Sanders, came out in much greater numbers than expected and he ran up large vote totals outside metro Detroit compared with Clinton. It was a signature surprise win for Sanders and one that Nate Silver, the founder of FiveThirtyEight.com, which analyzes statistical and polling data, said could count among “the greatest polling errors in primary history.”

On Friday night before a rally at TCF Center in downtown Detroit, Sanders, when asked about a recent poll that showed him trailing Biden by 7 percentage points in Michigan before the March 3 Super Tuesday rout, noted that the polls had been wrong four years before.

"We’re going to work as hard as we can to win Michigan," he said.

And he has been doing so, with rallies in Detroit, Dearborn, Flint, Grand Rapids and Ann Arbor.

But the poll, which has a margin of error of plus or minus 4.9 percentage points, shows he may have a lot of ground to make up in a hurry. It shows a candidate who is not doing as well with younger voters or voters outside metro Detroit as he did in 2016, when his campaign was riding a sudden wave of energy and enthusiasm.

It also shows a lot of late-breaking support for Biden as other candidates – former New York Mayor Mike Bloomberg, former South Bend, Indiana, Mayor Pete Buttigieg and Sen. Amy Klobuchar of Minnestoa – got out of the race and endorsed him.

"I believe the numbers," Porn said.

Support among younger voters there but may not be enough

Four years ago, the poll heading into the weekend before the primary showed that Sanders, a democratic socialist running an insurgent campaign against Clinton, held a clear edge with younger voters, taking 65% of their support. But they were expected to make up just 11% of the primary date electorate.

Instead, according to exit polls, voters aged 18-29 made up nearly 20% of the electorate and voted overwhelmingly for Sanders – 81%-19% – compared with Clinton. Meanwhile, turnout among older voters was down somewhat from what was expected.

The new poll shows the youngest age group it measured – 18-34 – making up 21% of Tuesday’s electorate. Among them, Sanders is still ahead of Biden, 58%-17%, with a large number of undecided voters, 19%. If they all break toward Sanders on Election Day, it could help him close the overall gap with Biden quickly.

But Biden is winning every other age group. Looked at as two blocs – those under the age of 50 and those over – Sanders wins the younger bloc, 43%-33% with 15% undecided. Biden wins the older group 65%-14% with 11% undecided.

The older group, according to the poll, makes up 56% of the electorate, while the younger group makes up 44%.

That may help explain why Sanders is barnstorming the state, especially after media reports suggesting that in the early states that have voted already, he has failed to produce the larger turnout among young people he promised.

It’s coming down to who voters think can beat Trump

Projecting the outcome of Tuesday's primary based on polling is fraught with uncertainty, however.

For one thing, a new law making it far easier to vote by absentee ballot has resulted in some 600,000 ballots already having been cast. Depending on when the majority of those were sent, and which candidate appeared to have momentum at the time, those absentee ballots will play a key role.

More than 28,000 absentee ballots also have been re-voted with the rush of departures from the race in recent days, including Sen. Elizabeth Warren of Massachusetts. The Free Press has reported that the narrowing of the race has largely appeared to favor one candidate – Biden.

More:New voting rules could help both Biden, Sanders as Michigan's primary election looms

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In some cases, even potential Trump supporters were changing their ballots. One, a 59-year-old retired engineer in Novi whose first name is Rob – he declined to give his last name because he didn’t want to be publicly identified – had previously gotten a Republican ballot, but came into the clerk's office to void it and get a Democratic one, deciding he wanted to vote now for Biden.

"He might be someone I can vote for (in November)," he said.

The poll indicated that while Sanders had slightly more support than Biden, 50%-42%, among voters who decided whom to support more than a month ago, among those who actually sent in their ballots, Biden led with 70%. Sanders’ number was low enough not to register, suggesting his voters were waiting until Election Day to cast their ballots.

Meanwhile, among the 37% of respondents who decided in the last few days, Biden led overwhelmingly, 75%-18%, over Sanders.

The reason, said Porn, was electability.

Among the 34% of respondents who said a candidate’s most important quality was that he or she shared their personal views, Sanders was effectively tied for support, 38%-36% ,with Biden, with the rest either undecided (18%) or going to other candidates (8%) who have dropped out of the race.

Among the 57% who said the most important thing was beating Trump in November, Biden got 61% of the support, to 21% for Sanders. To Porn, that is a matter of many of Sanders’ proposals being seen as too radical and a sudden questioning of his campaign.

Christen Lesko-Brown, 34, of Livonia, is a Sanders supporter who said she sees it, too, even though she believes it is Sanders whose bold ideas for slowing climate change, making colleges tuition-free and putting in place a government health care plan that covers all Americans with no out-of-pocket expenses could draw new voters and more readily defeat Trump.

“Biden’s more of the typical, establishment candidate,” she said at a Dearborn rally on Saturday for Sanders. “People are more fearful of Bernie’s ideas … I think other people do (think Biden’s more electable).”

Racial differences appear to favor Biden

Biden’s resurgence in South Carolina on Feb. 29 and several other states has been credited to a wave of support from black voters. In North Carolina and Alabama, two states that voted on Super Tuesday that have sizable black populations, Biden won among blacks handily – with 62% of the black vote in North Carolina and 72% in Alabama.

In Michigan, according to the poll, Biden clearly wins among black voters, leading Sanders 46%-24%. But with 25% still undecided, the poll suggests that the level of support might not be as high as in other states.

In 2016, exit polls showed Clinton scored higher among African-Americans in Michigan, with 68% for Clinton compared with 28% for Sanders.

That may be part of the reason that both candidates were trying to shore up their standing with African Americans on Sunday, with Sanders announcing the endorsement of civil rights leader Jesse Jackson and Biden getting the endorsement of Sen. Kamala Harris of California, a former candidate herself who is set to appear at a Detroit rally for Biden Monday night.

The support among black voters also bodes well for Biden in another state voting Tuesday, Mississippi.

Biden also announced the launching of a $12 million media campaign across eight states, including Michigan.

While African-American support is key, however, Biden also has been winning lately among white voters, which has helped him score upsets in states such as Minnesota and Massachusetts, which were widely expected to be split between Sanders and Warren.

The poll showed whites in Michigan favored Biden 56%-26% for Sanders, with 9% going to other candidates and 10% undecided. Compare that to exit polls four years ago that showed Sanders winning among whites 56%-42%.

Sanders could still pull it out, however

Over the last two weeks, momentum has clearly shifted toward Biden, who has a lead in the delegate count at a time when the nomination map begins to favor him more than it does Sanders.

And the field also has narrowed drastically, almost entirely to Biden’s benefit. Instead of splitting more moderate, establishment voters with other candidates, such as Bloomberg, Buttigieg and Klobuchar, Biden appears to have them for himself.

But it is Sanders, not Biden, who can still claim to have won Michigan in an upset four years ago when polls were declaring him all but out of the race. It is Sanders who, presumably, comes into Tuesday’s balloting not only having put together a winning coalition in 2016, but with vastly improved name recognition and renowned surrogates such as Rep. Rashida Tlaib of Detroit and Rep. Alexandria Ocasio-Cortez of New York backing him. Ocasio-Cortez was headed to Ann Arbor on his behalf Sunday.

If turnout among younger voters supporting Sanders over-performs expectations again and the support of Biden’s older voters is less than what it’s projected to be on Election Day, Sanders could win again. The new poll and others – which are only snapshots of a representative random sample at a given point in time – could show levels of support that don’t show up at the polls, which is what counts in the end. Biden's momentum could, for some reason, suddenly falter, as Clinton's did.

The difference in 2020 compared with 2016, however, is also stark.

Four years ago, Clinton was widely expected to win without much trouble across the U.S., despite Sanders’ campaign, which unleashed an enthusiasm many – including Clinton – were surprised to see. At the same time, she was a deeply polarizing candidate, especially among younger voters and outside of urban areas in the North, which played into her loss in Michigan.

This time, no one is going to be surprised by Sanders, as his strengths and weaknesses, like Biden’s, have been on display for months. Before the South Carolina primary, he was the clear front-runner and widely expected to compete for, if not win outright, the Democratic nomination to face Trump. Now, everything has changed.

Michigan will be the first major state where the two face off against each other without the other candidates involved and important implications for both. A host of other important nominating states — Arizona, Florida, Ohio and Illinois — are just another week away.

Contact Todd Spangler attspangler@freepress.com. Follow him on Twitter@tsspangler.