Former Vice President Joe Biden Joe BidenThe Memo: Warning signs flash for Trump on debates Senate Republicans signal openness to working with Biden National postal mail handlers union endorses Biden MORE is off to a strong Super Tuesday start after he was declared the winner of the Virginia, North Carolina and Alabama primaries by networks immediately as polls closed in both states.

Exit polls suggested Biden was bolstered by heavy support from African American voters, a development that had previously boosted him in South Carolina and portends well for his chances in other Southern states holding primaries Tuesday.

Polls had shown a tight race between Biden and Sen. Bernie Sanders Bernie SandersSenate Republicans signal openness to working with Biden Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll Schumer, Sanders call for Senate panel to address election security MORE (I-Vt.) in Virginia and North Carolina as recently as last week.

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But Biden’s big victory in South Carolina gave him a burst of momentum that could help blunt the advantage Sanders likely will have when polls close in California later tonight.

Biden was boosted by a string of endorsements from high-profile Virginians, including Sen. Tim Kaine Timothy (Tim) Michael KaineThe Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep Catholic group launches .7M campaign against Biden targeting swing-state voters GOP senator to quarantine after coronavirus exposure MORE (D), former Gov. Terry McAuliffe (D), and Democratic Reps. Bobby Scott Robert (Bobby) Cortez ScottHouse passes bill to allow private lawsuits against public schools for discriminatory practices Pelosi: House will stay in session until agreement is reached on coronavirus relief This week: House returns for pre-election sprint MORE, Jennifer Wexton Jennifer Lynn WextonThe Hill's Campaign Report: Trump's rally risk | Biden ramps up legal team | Biden hits Trump over climate policy Trump campaign knocks Biden event: 'All they could manage is a virtual event' Republicans face worsening outlook in battle for House MORE and Don Beyer.

And he’s benefiting from strong support among African Americans, taking more than 70 percent support among black voters in Alabama. Alabama is more than 40 percent black and has the largest population of black voters out of all the Super Tuesday states.

Exit polls in Virginia showed Biden taking about 66 percent support among black voters there as well.

The Democratic electorates in Virginia and North Carolina, as well as states across the Deep South, are more than a quarter black, according to exit polls.

In 2016, Sanders failed to win any state that had a black population of more than 21 percent, and that dynamic appears to be hampering him on Super Tuesday.

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Sanders, however, has strong support from Latinos, who helped him to a big victory in the Nevada caucuses. That could come into play later tonight in California and Texas, the two largest delegate hauls of the primary season.

Biden’s victories in Virginia and North Carolina are also harmful to former New York City Mayor Michael Bloomberg Michael BloombergThe Hill's 12:30 Report - Presented by Facebook - Latest with the COVID-19 relief bill negotiations The Memo: 2020 is all about winning Florida The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support MORE, who launched his campaign after becoming worried that Biden looked like a weak front-runner.

Bloomberg invested and campaigned heavily in Virginia, visiting it more than any other Super Tuesday state. He spent more than $12 million in North Carolina.

Now Biden stands to win at least a plurality of North Carolina’s 110 delegates and Virginia’s 99.

Sanders, meanwhile, easily won the primary in his home state of Vermont, where 16 delegates were up for grabs.

Polls are still open in California, where 415 delegates are at stake, and Texas, which accounts for 228 delegates.

Sanders will be looking to run up the score in California, the largest delegate prize on the map.

All told, about 1,300 delegates will be awarded Tuesday, accounting for about one-third of all pledged delegates up for grabs.

A candidate must win 1,991 delegates to clinch the Democratic presidential nomination.

Updated at 8:07 p.m.