(CNN) Joe Biden's mission in the presidential bid he launched on Thursday is to prove he's not a man out of step with the times.

He must convince a Democratic Party pulsating with forces of youth, gender and racial diversity that is moving left on health care and college funding to ultimately turn to a traditional middle-of-the road nominee to take on President Donald Trump.

Biden is an aging white male, a physically expressive old-school pol with a nose for the ideological center who still believes a political opponent is not a blood enemy.

And his third try to finally reach the political summit comes at the one moment in American history when such qualities have turned into liabilities.

But Biden has one huge card to sell to Democrats desperate to oust Trump: He might be their best hope of beating the President, especially in the Midwestern, blue-collar heartland. And his experience and dignity could be the antidote to Trump's rage.

Biden enters the crowded primary after months of soul searching as a clear but not prohibitive front-runner.

Invoking America's better angels, Biden is offering experience and a character forged by tragedy to purge the scandals, lies and constitutional chicanery of the current President and to close the societal schisms he has widened.

"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," Biden said in a video announcing his candidacy released Thursday.

"The core values of this nation, our standing in the world, our very democracy, everything that has made America, America, is at stake."

The 76-year-old is in a strong position in national polls and early voting states. He will run as a centrist Obama-Biden Democrat anchored by strong union support.

He will lambaste Trump as a phony populist and a friend of Wall Street CEOs who hit the jackpot with the tax overhaul law.

Biden's hopes may depend on the idea that working class, union Democrats and moderates in the suburbs remain the backbone of the party. Though he will also have to appeal to radical young progressives electrified by Rep. Alexandria Ocasio-Cortez of New York.

"The fact of the matter is, the vast majority of the members of the Democratic Party are still basically liberal to moderate Democrats in the traditional sense," Biden said last month while analyzing the 2018 midterm elections.

"Show me the really left-, left-, left-wingers who beat a Republican. So the idea that the Democratic Party has kind of stood on its head, I don't get."

"I'm an Obama-Biden Democrat man, and I'm proud of it," he added.

Biden will also claim progressive credentials, by pointing out his embrace of same-sex marriage before President Barack Obama -- and his authorship of the Violence Against Women Act in 1994.

Biden must also avoid the self-sabotage that doomed his campaigns in 1988 and 2008.

He needs to show the political fastball last called upon in a vice-presidential debate in 2012, which steadied Obama's suddenly wobbling re-election campaign.

Biden will have to reconcile his record on criminal justice, race and America's foreign wars with a party that has changed considerably even since he left office in January 2017.

Hanging over his bid is his anemic 2008 race, which he abandoned after polling less than 1% in Iowa.

A strong showing in the first-in-the-nation caucus is mandatory in 2020, since Sen. Bernie Sanders of Vermont is the reigning New Hampshire primary champion and Sen. Kamala Harris of California will test Biden's strong bonds with African Americans in South Carolina.

And Biden must show he can keep pace with top rivals and their small-donor fundraising brigades.

His supporters say the extreme circumstances of the Trump era cry out for his qualities.

"When Joe Biden looks in that mirror, he's not going to stop and not do this because it's going to be hard or he might lose or anything else," said Ted Kaufman, who served as Biden's chief of staff before succeeded him in the Senate.

"He does it because he won't feel right about himself that he had this opportunity and I personally believe a rare opportunity and a rare time in history for someone of his background, his experience to become President of the United States."

Why Biden might win

The former chairman of the Senate Judiciary and Foreign Affairs committees, who was in the room for Obama's every key decision, has more experience than the Democratic field combined.

He was seen as something of a punchline when he became vice president. But his loyalty, willingness to temper his political ego and safe hands on the stimulus plan and foreign policy won respect. He became beloved in the West Wing.

He even cut out most of his famous gaffes -- though he occasionally irked his buttoned-down boss, like when said into an open mic that passing Obamacare was a "big f***ing deal."

Biden will metaphorically stand shoulder to shoulder with Obama during his campaign -- given the ex-president's universal popularity among Democrats. Though Obama hailed his number two as a "brother" during his farewell address, there is no sign he will endorse Biden -- or anyone else -- during the primary.

If 2020 is about making Washington work and draining partisan poison, no one is better positioned than Biden: He even likes Senate Majority Leader Mitch McConnell, a Kentucky Republican.

If the test is meeting the slings and arrows of outrageous fortune, Biden has no peer.

Grief and resilience are never far from the surface in this compassionate, emotional man. He never hid his anguish over the loss of his first wife and infant daughter in 1972 and his son Beau in 2015 from brain cancer.

Biden's suffering has equipped him with the kind of genuine empathy many politicians have to fake.

He will stress decency, honesty and brotherly love, attributes that his supporters see personified in their candidate -- and that could strike a contrast with Trump.

"Folks, this is not who we are," Biden said before the midterms.

For better or worse, his charisma and name recognition mean he will have no trouble standing out from the Democratic crowd. He showed in 2008 that he's a formidable debater.

And he's spoiling to fight Trump. Biden said last year that if the pair were in high school he would "beat the hell out of him."

But the reason why some Republican strategists believe Biden could pose a strong threat is his appeal to the very voters who put Trump in the White House.

His hammy fables of the loving-yet-austere upbringing of little Joey Biden in his idealized birthplace of Scranton, Pennsylvania, are easy to mock. For years, he has dispensed hokey sayings about his mom, who he eulogized in 2010 as "Heroic in her ideals but solid in her expectations," and his dad, an unlucky businessman.

"Don't tell me what you value, show me your budget and I'll tell you what you value," he roars on the campaign trail, using one of Biden senior's sayings to show his understanding of the economic struggle of many Americans.

In retrospect, there are now many Democrats who think he would have done a better job than Hillary Clinton.

He would have camped out in states like Michigan and Wisconsin where Clinton was an infrequent visitor and Trump won the economic and cultural argument.

He would have pushed Trump, a New Yorker, in his native Pennsylvania.

David Urban, who masterminded Trump's triumph in the Keystone State, admits Biden has appeal, though he says Clinton already failed in running for "the third term of the Obama administration."

"I do think that Joe Biden speaks to a demographic in America that Democrats have to win back, if they want to win the Electoral College map and all of those states kind of in the middle there, Pennsylvania, Ohio," Urban said on CNN's "The Lead" this week.

Why Biden might lose

Biden's most obvious liability is age.

As soon as he lowers his hand after taking the oath of office, the then-78-year-old Biden would be the oldest President in American history. Ronald Reagan was 77 at the end of his second term.

Biden, a teetotaler who sometimes breaks into a trot before the cameras to showcase his fitness, is a well-preserved septuagenarian. And the age issue would not matter in a match-up with Trump, who's 72.

But he is asking Democrats not to embrace a new generation of leadership in the primary and even to turn back the clock.

The youngest Democratic candidate, South Bend, Indiana, Mayor Pete Buttigieg, is not even half Biden's age.

It's poignant that Biden faces this question. Because he was the future once. He was a pearly toothed Democratic young gun when Delaware made him one of the youngest senators in history.

Biden, captured by Richard Ben Cramer in the campaign classic "What It Takes," was the kid who beat a paralyzing stutter to acquire a gift for gab.

But his loquaciousness undid him when he had to drop out of the 1988 race after using unattributed quotes by former British Labour Party leader Neil Kinnock.

Amid complaints by several women in recent weeks that he had invaded their personal space, Biden's foot seemed to be back in his mouth. He joked twice about having permission to touch people before delivering a speech.

Biden cannot afford to alienate female voters, given the strong sense in the party that it's a female candidate's turn again after Clinton's narrow failure to shatter the glass ceiling.

He will also have to court African American women -- a crucial Democratic constituency. Biden's team was warned this week not to launch his campaign on Wednesday -- the same day as the She the People forum devoted to women of color.

If he can deal with age and gender problems, Biden's longevity could still be an issue.

He has a longer Washington record than any successful Democratic nominee for the last five decades. So he must brace for a 40-year opposition research dump.

Already, Biden has been criticized for his handling of sexual harassment allegations by Anita Hill against Justice Clarence Thomas during Thomas' confirmation hearings in 1991.

And his authorship of a criminal justice bill in the same decade was blamed for sparking mass incarceration -- an issue especially important to African American voters.

Biden admitted in January that he hadn't "always been right" on the issue. He's also been close to the finance industry in Delaware, a factor that could undermine his economic arguments. He voted in 2002 to authorize the Iraq War, another no-no for Democrats. Then again, so did Clinton.

And his record of reaching across the aisle could antagonize liberals fulminating against Republicans.