Barack Obama will formally endorse Joe Biden for president

• Former President Barack Obama will formally former Vice President Joe Biden in the 2020 election on Tuesday, NBC News reported.
• Biden became the presumptive Democratic nominee last week after Vermont Sen. Bernie Sanders dropped out of the 2020 race.
• Obama held off on endorsing any one Democratic candidate when the primary field was more crowded.
• But several aides told Politico the former president worked behind the scenes to help Biden's campaign when it was working to clinch more endorsements.
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Former President Barack Obama will formally endorse former Vice President Joe Biden in the 2020 election on Tuesday, NBC News reported.

Biden became the presumptive Democratic nominee last week after Vermont Sen. Bernie Sanders dropped out of the 2020 race.

Sanders also endorsed Biden on Monday, saying in a livestreamed video with Biden, "We've got to make Trump a one-term president, and we need you in the White House."

Obama held off on endorsing any one Democratic candidate when the primary field was more crowded. But several aides told Politico that he worked behind the scenes to "nudge things in Biden's direction when the Biden team was organizing former candidates to coalesce around Biden."

Indeed, one Obama adviser described the day Sanders dropped out to Politico as a "very good day!"

The former vice president's campaign got off to a rocky start with a series of disappointing finishes in the early primary and caucus states. But Biden surged to the front of the Democratic pack with resounding victories on Super Tuesday and in later contests. He also got a boost when other centrist Democratic candidates who shaved off some of Biden's support dropped out and endorsed him.

Massachusetts Sen. Elizabeth Warren is the only former candidate who hasn't yet made an endorsement in the election.

Biden has leaned heavily on Obama's legacy throughout his 2020 campaign, positioning himself as the candidate best suited to carry the mantle for the Democratic Party. Biden's connection to Obama played a significant role in helping him garner the support of black voters, who make up a huge voting bloc for the party.

"Most of America knows Joe Biden as the vice president to the first black president in history. And black voters especially look at President Obama and say if Biden is good enough for Obama to trust, then who am I to sort of question that?" Theodore Johnson, a senior fellow at the Brennan Center for Justice, told NPR in March.

"And so for an electorate where the most important thing is beating Donald Trump in November - and Trump's disapproval rates among African Americans is exceptionally high - Biden presents as the person that can do that not just because of his ability to win the African American vote," he added.

The former vice president touted his ties to Obama on a number of signature campaign issues including immigration,