The announcement marks Obama’s highly anticipated foray into the 2020 race after declining to back a candidate during the primary contest, and comes just one day after Vermont Sen. Bernie Sanders also endorsed Biden’s candidacy.

Obama’s endorsement, while widely expected, also represents a new phase in the general election campaign against President Donald Trump, unlocking the Democratic Party’s most powerful surrogate for Biden at a time when his campaign has struggled to cultivate momentum amid the outbreak of the coronavirus in the U.S.

Although Biden maintained during the primary that he had asked Obama not to endorse any particular Democratic candidate — insisting that “whoever wins this nomination should win it on their own merits” — he relentlessly invoked his eight years of service under the former president and close personal relationship with him to court voters.

Biden’s efforts to align himself so closely with Obama, even as the previous administration’s policies came under occasional scrutiny from the party’s left flank, were ultimately successful in propelling him past more progressive rivals to become Democrats’ pick to challenge Trump in November.

His tenure as Obama’s No. 2 also contributed immeasurably to Biden’s firewall of support among African-American voters and proved foundational to the campaign’s argument that the former vice president was a capable, experienced leader ready to assume the responsibilities of the Oval Office.

Weighing in on the endorsement Tuesday, Brad Parscale, Trump’s reelection campaign manager, asserted that Obama “spent much of the last five years urging Joe Biden not to run for president out of fear that he would embarrass himself,” and now “has no other choice but to support him.”

“Obama was right in the first place: Biden is a bad candidate who will embarrass himself and his party,” Parscale said in a statement. “President Trump will destroy him.”

As a historically crowded and diverse field of White House hopefuls competed for the Democratic nomination over the past year, Obama’s public statements and remarks on the state of the race were closely parsed for potential clues regarding his preference of candidate and hopes for the future of the party.

When Biden officially entered the race last April, the former president’s spokeswoman said Obama “relied on the vice president’s knowledge, insight and judgment throughout both campaigns and the entire presidency,” and added that the two men “forged a special bond over the last 10 years.”

In November, Obama memorably warned a group of liberal donors that the “average American doesn’t think we have to completely tear down the system and remake it,” arguing that voters “just don't want to see crazy stuff” and “are not driven by the same views that are reflected on certain, you know, left-leaning Twitter feeds.”

He also reportedly urged Democrats later that same month to “chill out” about the party’s pool of candidates and expressed suspicion toward “purity tests during elections.”