WASHINGTON — Former Vice President Joe Biden launched his third bid for the presidency on Thursday, positioning himself as a trusted champion of the middle class eager to take the fight to President Donald Trump.

In a video released early Thursday morning, Biden said that "we are in a battle for the soul of this nation."

In the video's opening, Biden highlighted the 2017 violence in Charlottesville, Virginia, where during a large gathering of white nationalists and counterprotesters a white supremacist rammed his car into an opposition group, killing one person.

Biden noted that President Donald Trump said there were some "very fine people on both sides" in Charlottesville, where the white nationalists were protesting the city's plan to take down a statue of Robert E. Lee, a Confederate general.

"In that moment, I knew the threat to this nation was unlike any I'd seen in my lifetime," Biden said, adding that he believes "history will look back on four years of this president and all he embraces as an aberrant moment in time."

"But if we give Donald Trump eight years in the White House, he will forever and fundamentally alter the character of this nation," Biden continued. "Who we are. And I cannot stand by and watch that happen."

The core values of this nation… our standing in the world… our very democracy...everything that has made America -- America --is at stake. That’s why today I’m announcing my candidacy for President of the United States. #Joe2020 https://t.co/jzaQbyTEz3 — Joe Biden (@JoeBiden) April 25, 2019

A spokesperson for former President Barack Obama told NBC News that Biden "has long said that selecting Joe Biden as his running mate in 2008 was one of the best decisions he ever made."

"He relied on the vice president’s knowledge, insight and judgment throughout both campaigns and the entire presidency," the spokesperson continued. "The two forged a special bond over the last 10 years and remain close today."

A source familiar with Obama's thinking said the ex-president is "excited by the extraordinary and diverse talent" in the Democratic primary field and that "it’s unlikely that he will throw his support behind a specific candidate this early in the primary process."

Speaking briefly with reporters after getting off an Amtrak train in Wilmington, Delaware, Biden said he asked Obama not to make an endorsement.

"Whoever wins this nomination should win the nomination on their own merits," Biden said.

Biden has hired at least 30 staff members in recent days, including Symone Sanders, the former spokesperson for Vermont independent Sen. Bernie Sanders' 2016 presidential campaign.

Trump tweeted Thursday morning about Biden joining the large Democratic primary field, saying, "Welcome to the race Sleepy Joe."

"I only hope you have the intelligence, long in doubt, to wage a successful primary campaign," the president continued. "It will be nasty — you will be dealing with people who truly have some very sick & demented ideas. But if you make it, I will see you at the Starting Gate!"

Biden's long-anticipated entry into the jam-packed 2020 Democratic field comes almost four months after Sen. Elizabeth Warren of Massachusetts became the first big-name Democrat to take her initial steps toward a run, but with a marathon 41 weeks left until the first-in-the-nation Iowa caucuses.

The former two-term vice president and six-term senator from Delaware enters as the putative front-runner, at or near the top of every state and national poll, and with a recognized political brand cultivated during almost a half-century in public office.

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But he faces serious obstacles in his bid for the Democratic nomination, including a restive and vocal liberal base, his past policy positions on major issues, and a campaign infrastructure being built in real time. And at 76, he's older than almost all of the 19 other Democrats in the race so far.

One of Biden’s first acts as a declared candidate, in fact, will be to attend a high-dollar fundraiser in Philadelphia on Thursday evening — reflecting an urgent need to catch up financially to the rest of the field. The fundraiser is taking place at the home of David Cohen, the senior executive president of Comcast Corp., the parent company of NBC News.

His team is also working to quickly build a digital infrastructure to grow an online, grassroots supporter base that can fuel the campaign with small-dollar donations.

Biden's first public scheduled event will come Monday afternoon in Pittsburgh, where he will speak to members of the Teamsters union about rebuilding the middle class. He'll then travel to early primary and caucus states before wrapping up his launch week back in Philadelphia, where advisers say he will lay out a vision of bringing Americans together in a polarized time during a May 18 rally.

The video, Pittsburgh and Philadelphia rallies each focus on one of what advisers say are the three core pillars of Biden's candidacy: the battle for the soul of the nation, rebuilding the middle class, and bridging the country's divides.

Biden is relying heavily not only on the support of organized labor to secure the nomination, but also to get his campaign off the ground. In addition to the Teamsters event in Pittsburgh, the International Association of Fire Fighters is slated to meet in the next 24 hours to make its expected endorsement official.

Biden's strength and popularity in polls can only be partially explained by his universal name recognition, since other candidates, such as Sanders, are almost as well known but have lower favorability ratings.

Biden, who was elected to the Senate at 29 in 1972, ran for the Democratic presidential nomination in 1988 and 2008, but earned the second spot on the presidential ticket and then eight years in the White House with Obama. Biden seriously considered challenging Hillary Clinton for the nomination in 2016, but ultimately decided to forgo a run in the wake of his son Beau's death to cancer. The loss hit Biden hard and he wrote a book about his grief, "Promise Me, Dad: A Year of Hope, Hardship, and Purpose."

Senate Judiciary Committee Chairman Joe Biden, D-Del., points angrily at Clarence Thomas during comments at the end of hearings on Thomas' nomination to the Supreme Court on Capitol Hill in 1991. Greg Gibson / AP file

It was the second major family tragedy of Biden's life. A few weeks after he was elected to the Senate, his wife and infant daughter were killed in a car crash while Christmas shopping. Biden's two sons, Beau and Hunter, were in the backseat and injured, but OK. He married his current wife, Jill, five years later.

Biden's association with the still-popular Obama will likely be front-and-center in his candidacy, even if he doesn't have Obama's explicit endorsement.

"I'm an Obama-Biden Democrat, man. And I'm proud of it," Biden said last month.

His pitch will be aimed not at the most vocal progressive activists in the party, but at what advisers see as a much larger pool of pragmatic and independent voters to whom, they feel, Biden has a unique appeal.

He has been considering policy proposals designed to restore what he often calls the "basic bargain" with the middle class, including a tax rewrite that would help fund free community college, an increased minimum wage and a major infrastructure push.

Biden's decades of experience crafting American policy have made him, as he argued in December, "the most qualified person in the country to be president." But it's also left a paper trail of votes and statements from other political eras that his campaign opponents are sure to weaponize against him.

Over his long career, Biden has taken positions on a wide range of issues — from busing to banking — that could be liabilities in today’s more racially sensitive and economically progressive Democratic Party. Biden is known to be affectionate, but in the #MeToo era, several women have also come forward to say that he made them feel uncomfortable by touching them.