WASHINGTON (AP) - Declaring the "soul of this nation" at stake, former Vice President Joe Biden pushed into the crowded 2020 presidential contest on Thursday and quickly sparked a fierce debate over the direction of the modern-day Democratic Party.

Ignoring the political noise in his own party, Biden aimed directly at Donald Trump in an announcement video seizing on the Republican president's response to the deadly clash between white supremacists and counter protesters in Charlottesville, Virginia two years ago. That was the spur for him to launch a third presidential bid, Biden said, noting Trump's comments that there were some "very fine people" on both sides of the violent encounter, which left one woman dead.

"We are in the battle for the soul of this nation," Biden declared. "If we give Donald Trump eight years in the White House, he will forever and fundamentally alter the character of this nation - who we are. And I cannot stand by and watch that happen."

Yet Biden will get a chance to take on Trump only if he survives a Democratic field that now spans at least 20 contenders. And his party's more liberal wing was far from welcoming in the hours immediately after he declared his candidacy. Justice Democrats, a group created from the remnants of Bernie Sanders' failed 2016 campaign, came out against Biden on Thursday and spent much of the day assailing him on social media.

As an older white man with often-centrist views, Biden must now prove he's not out of step with Democrats trying to push the party to the left.

He's been taking steps in recent weeks to clean up perceived missteps from his long record in elected office, including his role as a senator in allowing sexual harassment accuser Anita Hill to be grilled by an all-male committee during the Clarence Thomas Supreme Court confirmation hearings.

A campaign aide said Biden has privately contacted Hill to share "his regret for what she endured and his admiration for everything she has done to change the culture around sexual harassment in this country." But The New York Times reported Thursday that Hill said in an interview she was "deeply unsatisfied" and unconvinced by his apology.

Biden has also highlighted his role in authoring the Violence Against Women Act nearly three decades ago, legislation that is credited with reducing domestic violence nationwide.

Still, the 76-year-old Scranton-Pennsylvania native's political liabilities are many.

He would be the oldest person ever elected president - Trump was 70 in 2016 - even as his party embraces a new generation of diversity. He's also yet to outline his positions on issues defining the 2020 Democratic primary, most notably "Medicare for All," the universal health care plan authored by Sanders that has been embraced in one form or another by virtually the entire Democratic field.

Biden is betting that his working class appeal and ties to Barack Obama's presidency will help him win over skeptics. He quickly racked up endorsements on Thursday morning, becoming the first Democrat running for president with the backing of more than one U.S. senator.

Rep. Cedric Richmond, D-La., who previously served as chairman of the Congressional Black Caucus, said he had urged the former vice president to run and highlighted Biden's potential electability when asked to assess African Americans' feelings.

"Black voters are saying the same thing that white Democrats are saying: We can't afford to lose. That is a big message. That's a big motivator," Richmond said.

Obama has so far declined to endorse Biden, however, and several former Obama aides are now working for other candidates. Biden addressed Obama's position as he briefly faced reporters in Delaware on Thursday.

"I asked President Obama not to endorse," Biden said. "Whoever wins this nomination should win it on their own merits."

While he didn't endorse, Obama took the unusual step of weighing in on Thursday's announcement.

"President Obama has long said that selecting Joe Biden as his running mate in 2008 was one of the best decisions he ever made," Obama spokeswoman Katie Hill said. "He relied on the vice president's knowledge, insight and judgment throughout both campaigns and the entire presidency. The two forged a special bond over the last 10 years and remain close today."

Trump was quick to pounce on Biden, who he has nicknamed, "Sleepy Joe."

"I only hope you have the intelligence, long in doubt, to wage a successful primary campaign," Trump said. "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."

Privately, Trump allies have warned that Biden might be the biggest re-election threat given the former vice president's potential appeal among the white working class in the Midwest, the region that gave Trump a path to the presidency.

Biden is paying special attention to his native Pennsylvania, a state that swung to Trump in 2016 after voting for Democratic presidential candidates for decades. While Biden represented Delaware in the Senate for 36 years, he was often referred to as Pennsylvania's third senator.

The former vice president will be in the state three times within the opening weeks of his campaign. He'll be in Philadelphia on Thursday evening headlining a fundraiser at the home of David L. Cohen, executive senior vice president of Comcast. Biden was aiming to raise $500,000 at the event.

He will hold his first public event as a 2020 presidential candidate in Pittsburgh on Monday. Then it's off to Iowa, home of the leadoff nominating caucuses on Tuesday and Wednesday, followed by two days in South Carolina. He'll visit the other two early-voting states, Nevada and New Hampshire, in early May, before holding a major rally in Philadelphia.

Biden's first media appearance is set for Friday morning on ABC's "The View," a move that may help him make an appeal to women whose support will be crucial to winning the primary. He also hired Symone Sanders to serve as a senior strategist, tapping a prominent African American who previously worked for Biden's chief competitor, Bernie Sanders, in the 2016 presidential contest.

As Biden neared his campaign launch, his challenges have come into greater focus.

He struggled last month to respond to claims that he touched 2014 Nevada lieutenant governor nominee Lucy Flores' shoulders and kissed the back of her head before a fall campaign event. A handful of other women have made similar claims, though none has alleged sexual misconduct.

Biden, a former U.S. senator from Delaware, pledged in an online video to be "much more mindful" of respecting personal space but joked two days later that he "had permission" to hug a male union leader before addressing the group's national conference.

On another issue he'll have to address throughout the campaign, Biden once played a key role in anti-crime legislation that had a disproportionately negative impact on African Americans. And last month he struggled to explain comments he made as a freshman senator in 1975 about the school busing debate.

Despite the challenges, his high-profile status in the race may make it difficult for his competitors. New Jersey Sen. Cory Booker cast Biden's announcement as a direct threat to his own campaign in a fundraising appeal.

"The truth is this poses a real challenge for an underdog campaign like ours," Booker said.