WASHINGTON – Former President Barack Obama, who remained neutral for the entirety of the 2020 Democratic primary, endorsed his former vice president, Joe Biden, on Tuesday.

"I’m so proud to endorse Joe Biden for president of the United States," Obama said in a nearly 12-minute video statement. "Choosing Joe to be my vice president was one of the best decisions I ever made, and he became a close friend. And I believe Joe has all the qualities we need in a president right now."

Obama said he is going to hit the campaign trail for Biden "as soon as I can."

Biden tweeted shortly after Obama's remarks became public, saying the endorsement "means the world to Jill and me."

"We’re going to build on the progress we made together, and there’s no one I’d rather have standing by my side," Biden said.

Obama had stayed mum on endorsing a candidate throughout the Democratic primary, saying voters must pick the nominee. After Sen. Bernie Sanders suspended his campaign last week, the primary election effectively came to an end, and Biden is the presumptive Democratic nominee.

There have been questions for months about when or if Obama would weigh in on the primary, especially during the early state primary and caucus contests in which Biden placed lower than anticipated.

Obama, who tied with President Donald Trump for the most admired man in America in a Gallup poll this year, is the most popular Democrat, according to YouGov. He had large support among young voters, a group that Biden has struggled to reach throughout the primary cycle. Obama's endorsement could help the former vice president grow support among that voting bloc and encourage young voters to turn out.

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According to polling and election data, Biden has overwhelming support from black voters. Some black voters pointed to his history of support for their community and his relationship with Obama. Biden has received the endorsement of several black leaders, such as Rep. Jim Clyburn, D-S.C., and civil rights icon Rep. John Lewis, D-Ga.

"I know Joe Biden as a man of character and dignity," Lewis said in his endorsement statement. "A man who cannot, and will not rest when he sees injustice in our American home."

Throughout the campaign, Biden has invoked Obama’s legacy, noting that he would build on the Affordable Care Act, colloquially called Obamacare. The health care legislation is one of the Obama’s biggest accomplishments as president.

As the USA reels from the coronavirus pandemic, Biden touted his and Obama’s efforts when they were in office to keep Ebola from overwhelming the country.

During his endorsement remarks, Obama referred to the coronavirus pandemic and highlighted Biden's work during the H1N1 and Ebola outbreaks.

“Joe helped me manage H1N1 and prevent the Ebola epidemic from becoming the type of pandemic we’re seeing now," Obama said. "He helped me restore America’s standing and leadership in the world on the other threats of our time, like nuclear proliferation and climate change."

Obama tried to assure Sanders supporters that Biden is liberal enough, particularly on health care.

The former president said it's "time to go further" than Obamacare.

"We should make plans affordable for everyone, provide everyone with a public option, expand Medicare and finish the job so that health care isn’t just a right, but a reality for everybody," he said.

Biden has been critical of Sanders' proposed "Medicare for All," which calls for a single-payer system.

“There’s too much unfinished business for us to just look backwards, we have to look to the future," Obama said. "Bernie understands that. And Joe understands that."

Obama noted that a Biden administration would "go much further" on climate change.

"We have to return the U.S. to the Paris Agreement and lead the world in reducing the pollution that causes climate change," Obama said. "But science tells us we have to go much further – that it’s time for us to accelerate progress on bold new green initiatives that make our economy a clean energy innovator, save us money and secure our children’s future.

"Of course, Democrats may not always agree on every detail of the best way to bring about each and every one of these changes," Obama continued. "But we do agree that they’re needed. And that only happens if we win this election."

On the campaign trail, Biden has noted how he was still in contact with the former president. Biden said during a virtual fundraiser that he turned to Obama for advice on choosing a vice presidential candidate, according to a pool report of the event. Biden said Obama told him to find someone who has experience where the former vice president is lacking, a dynamic that worked well between the two.

“And so I'm going to need a woman vice president who has the capacity, has strengths where I have weaknesses,” Biden said during remarks at the virtual fundraiser, according to the pool report.

Obama's endorsement is not the first time he has spoken out during the 2020 primary election. In March, Obama demanded South Carolina television stations and a pro-Trump group stop airing an advertisement that used his voice to attack Biden.

The ad, aired by the Committee to Defend the President super PAC, includes audio of Obama reading from his memoir, "Dreams from My Father," about Democrats who court black voters only at election time. In the book, Obama paraphrased the words of someone else.

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Obama spokeswoman Katie Hill, in a statement, called the ad "despicable."

“President Obama has several friends in this race, including, of course, his own esteemed Vice President," she said in the statement.

Trump questioned why Obama didn't endorse Biden early on in the campaign.

"I don't know why President Obama hasn't supported Joe Biden a long time ago," Trump said at a coronavirus briefing, claiming that Obama "feels something is wrong."

"It does amaze me that President Obama hasn't supported Sleepy Joe. It just hasn't happened. When's it gonna happen? Why isn't he? He knows something that you don't know, that I think I know, that you don't know," the president speculated. He did not elaborate.

Contributing: John Fritze