Sanders, Biden face the first major test as voters head to the polls in newly two-person race

The second round of major voting begins Tuesday as voters head to the polls to weigh in on the Democratic primary-- a contest which includes the key battleground state of Michigan.

In that state as well as Missouri, Mississippi, Idaho, North Dakota and Washington state voters will have their say on the presidential race on Tuesday, with 352 delegates up for grabs across the six states.

With the field narrowed down to what is ostensibly a two-person race between former Vice President Joe Biden and Sen. Bernie Sanders, I-Vermont, the race is looking similar to the dynamics at play during the Democratic showdown of 2016. Biden, a moderate Democrat backed by the establishment, is facing off with Sanders, a progressive-standard-bearer who is calling for a dismantling of many governmental structures.

Biden, the apparent front-runner ahead of Tuesday’s elections, has nabbed consequential endorsements since his Super Tuesday blowout, a sign that major factions of the party united behind one candidate-- that isn’t Sanders.

“Democrats need a nominee who understands that the way to beat Donald Trump is to bring people together,” former Secretary of State John Kerry said while stumping for Biden in Dearborn, MI on Saturday.

Biden has pointed to his growing list of endorsements from moderates as a sign that he is better equipped to take on the White House, arguing that he is the only candidate who can beat Trump. His former competitors Sen. Cory Booker, D-NJ, and Sen. Kamala Harris, D-Calif, endorsed him over the weekend.

Kerry echoed that message onstage in Dearborn over the weekend.

“I would say to them, are you going to throw your vote away? Are you gonna vote for somebody who is not going to be able to do what he's talking about? Or are you going to vote for somebody who's actually going to be able to fix America?” he asked the crowd.

Sanders, meanwhile, is trying to repeat the shocking upset he pulled out in Michigan in 2016, where he eked out a win from underneath Clinton-- who was almost assuredly thought to win the state during the primary contests.

"Michigan is very, very important. Last time around, in 2016, I was told, 'Impossible. You can't win Michigan.' In fact, the day before the election, we were 20 points down in some of these polls," Sanders said on ABC News’ This Week with George Stephanopoulos on Sunday.

Michigan is the first diverse, industrial Midwestern state to weigh into the primary, and the first 2020 battleground that will be crucial in making the electability argument against Trump in November. It also has the most delegates up for grabs on Tuesday with 125.

It is also the only state which allows voters to spoil their ballots, should they change their minds or the candidate they voted for leaves the race. Since the exodus from the Democratic race, which began following the primary in South Carolina, nearly 30,000 Michigan voters have spoiled their ballots and cast new ones.

“This is a very, very important day. And Michigan is the most important state coming up on Tuesday,” Sanders said in Ann Arbor on Saturday. As he seeks to regain the delegate lead, Michigan is a must-win for the Vermont senator and a chance to prove that he can amass more support from black voters than Biden.

That depends on how much of the vote Sanders can turnout on Tuesday, though Biden argued over the weekend that his coalition is the one which will compel people to head to the polls-- and eventually will be the one to remove President Trump from office.

“Senator Sanders likes to say he'll need a record turnout to defeat Donald Trump. He's right. And we’re the campaign that’s gonna do that record turnout,” Biden said at a campaign rally in St. Louis, MO on Saturday.

Across a few northern states that have cast ballots so far, Biden has beaten Sanders among one of the groups that was key to Sanders defeating Clinton in Michigan. In Massachusetts, Minnesota and Maine on Super Tuesday, Biden clinched 42%, 44% and 36% of white, non-college educated voters, compared to Sanders' 34%, 32%, and 33% respectively.

Exit polls from Super Tuesday states show Biden’s strength with black voters and moderates of all ages, although Sanders continues to soar among young voters and Hispanics. He’ll need more young voters to turn out to balance Biden’s grip on the older Democratic electorate.

Like Michigan, black voters made up 21% of Missouri’s Democratic electorate in 2016, meaning that Biden would need to maintain or surpass Clinton’s 2016 numbers.

In Mississippi, Biden is likely to take home a win after his all-star showing in the South and states with large black electorates. Black voters in the state comprise 71% of the Democratic electorate.

In contrast, Sanders ran away with the vote from mostly-white the Washington state caucuses in 2016. The caucus format has traditionally been successful for Sanders, as he took home the vote in Idaho and North Dakota in 2016 as well.

All three of those states have since abandoned the caucus system and moved to primaries.

All polls will be closed by 11 p.m. ET.

This report was featured in the Tuesday, March 10, 2020, episode of “Start Here,” ABC News’ daily news podcast.

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