Biden's endorsement rollout has one goal: To show him as the leader of a newly unified party

Biden on Tuesday won the public embrace of his most significant supporter yet: former president Barack Obama. In a video that served as part endorsement and part political blueprint, Obama called on Americans to unite in a"great awakening" in November and attested that his former vice president "has the character and the experience to guide us through one of our darkest times and heal us through a long recovery."

Obama's support, complete with criticism of his successor, came a day after Sen. Bernie Sanders, I-Vt., the second-place finisher in the Democratic nominating contest, endorsed Biden and condemned Trump.

Other party leaders are expected to soon join them. Sen. Elizabeth Warren, D-Mass., another former rival, plans to throw her support to Biden in the near future, according to a person with knowledge of her plans who spoke on the condition of anonymity because the person was not cleared to discuss those plans publicly. Hillary Clinton, the party's last nominee, also is expected to back Biden soon, according to a person familiar with her thinking who also spoke on the condition of anonymity to discuss campaign strategy.

The endorsements have been meticulously spaced out and delivered through prerecorded video, tweets and live-streamed discussions that have replaced rallies and town halls in the campaign-curbing era of the coronavirus.

Already the endorsements have substantially expanded Biden's reach, which he has struggled with given the restrictions that have left him captive in his basement video studio as Trump has free rein over the nation's air waves. In about six hours, Obama's video had racked up more than 5 million views on Twitter and hundreds of thousands of more clicks on YouTube. The video Biden posted of his joint live stream with Sanders had garnered 672,000 views on Twitter by Tuesday afternoon.

"Every day it's a couple more - rather than, here's a list of 500 people that have endorsed Biden," said Rep. Don Beyer, D-Va., who served as an ambassador under Obama and is helping Biden raise money.

"Having Bernie and Obama - two very different people," Beyer added, "makes a lot of difference."

The week's endorsements also have reflected different wings of the party - which have clashed openly in recent years - that Biden's campaign needs to help energize voters in the fall. Obama's moderation has grated on some of Sanders' loyalists, who in turn have drawn the ire of Biden supporters.

But now, as the week was intended to illustrate, they are joined in service to upending Trump from their distinct bases of power. Obama's resonance with African-American voters is without equal. Sanders commands a loyal following of young people and liberal activists. And Clinton and Warren share an appeal to suburban women, another key November demographic.

The effort to bolster Biden will reach its peak in a looming decision: Who will he choose as his vice presidential running mate?

Already there are competing pressures in the party over the choice, which some regard as the most consequential pick for a candidate in years, due to Biden's age (77). Biden has said his running mate will be a woman.

Some party leaders favor selecting someone who projects youth. Others value a running mate who has shown leadership in the coronavirus crisis or would add ethnic diversity to the ticket.

"I think he will pick a woman of color, either Hispanic or black. Certainly no one's told me that. That's just my thought," former Senate majority leader Harry Reid, D-Nev., said in a telephone interview last week.

On Tuesday, however, Biden's focus was on the man who he served as running mate beginning more than a decade ago. In a 12-minute video that constituted Obama's most detailed comments this year on the election, the 44th president sought to hit unifying notes. He tied his support of Biden to the coronavirus pandemic, issued a blistering critique of the Republican Party and nodded to the rivals Biden vanquished in the primary, which he said featured "one of the most impressive Democratic fields ever."

The public health crisis has "reminded us that government matters. It's reminded us that good government matters, that facts and science matters," Obama said.

Although he did not name Trump, he issued a stern warning to voters: "The Republicans occupying the White House and running the U.S. Senate are not interested in progress. They are interested in power."

To defeat them, Obama said, would require Americans uniting in a "great awakening against a politics that too often has been characterized by corruption, carelessness, self-dealing, disinformation, ignorance and just plain meanness."

The announcement served as Obama's public reemergence after a contest in which he largely stayed out of the spotlight as two dozen Democrats fought for the nomination. The former president remains perhaps the most popular and influential figure in the party, making his support the most sought-after stamp of approval in Democratic politics.

Ever since Biden effectively wrapped up the nomination last week, many Democrats have expected Obama's public nod. It came one day after former first lady Michelle Obama signaled a more public interest in the election, as she announced an initiative to expand vote-by-mail options.

As if seeking to overtly knit together his party, Obama devoted a part of his remarks to praising Sanders, who suspended his campaign last week, calling him "an American original" and "a man who has devoted his life to giving voice to working people's hopes, dreams and frustrations." While the two have not always agreed, Obama said, they are united in their pursuit of a more just society.

Obama also said that "even before the pandemic turned the world upside down, it was already clear we needed real structural change." Those words bore echoes of Warren's signature campaign theme, a call for "big structural change."

The former president effectively reflected arguments that Sanders and Warren had made in the campaign - that Democrats needed to move further left than he and Biden did in their administration on issues such as health care and climate change. He added that the coming recovery will require daring steps.

"For the second time in 12 years, we'll have the incredible task of rebuilding our economy. And to meet the moment, the Democratic Party will have to be bold," he said.

The week's moves did not salve all the Democratic divisions; neither Obama on Tuesday nor Biden, in his side-by-side video with Sanders on Monday, endorsed the Medicare-for-all health-care program advocated by many on the left. Olive branches extended by Biden late last week were deemed marginal by some on the left.

"I don't think it's enough, but I but I think it was a good start," said Aimee Allison, founder of the group She the People, speaking of Biden's appeals. She said she believes that Biden needs to strengthen his appeal to women of color and that his running mate "must be a black woman and must be someone who can appeal to and expand the base."

Added Rashad Robinson, speaking for the Color of Change PAC: "I still think he has work to do to shore up the next generation of the party. He has endorsements from the same people who endorsed the last nominee of the party."

Democratic pollster Stan Greenberg said his party remained "very divided" despite its deep opposition to Trump. He said he interpreted Biden's recent maneuverings as a recognition that "the party has to consolidate."

Many Democrats believe Obama is best equipped to make that happen. Throughout the campaign, Biden has emphasized his tenure in Obama's administration and his relationship with the former president. One of the first digital spots of the campaign was anchored around Obama's praise of him. At the time, senior Democrats saw Obama's silent consent to the ad as a sign of support.

Obama on Tuesday called his selection of Biden as his vice presidential pick one of "the best decisions I ever made."

Although Obama has kept a low profile in recent months, he has been in touch behind the scenes with the Democratic candidates, offering many of them advice and guidance and consulting with them at critical junctures.

Obama had conversations with Sanders and Biden over the past few weeks focused on defeating Trump, according to a person with knowledge of the talks who spoke on the condition of anonymity to discuss private conversations. He was said to be determined to play a role in unifying and energizing the party for the general election.

The former president also spoke with former South Bend, Ind., mayor Pete Buttigieg, a Democrat, and Sen. Amy Klobuchar, D-Minn., after they ended their campaigns last month, according to a person with knowledge of the talks.

The Trump campaign sought to play down the effects of Tuesday's endorsement. "Now that Biden is the only candidate left in the Democrat field, Obama has no other choice but to support him," Trump campaign manager Brad Parscale said in a statement.

But Democrats, emboldened by polls showing Biden ahead of Trump, said they were feeling increasingly optimistic.

"We don't know when the pandemic is over," said Beyer. "So having good news, in a political sense, news that binds us, news that makes us optimistic, that's really helpful."