(SOUNDBITE) (ENGLISH) U.S. DEMOCRATIC PRESIDENTIAL PRIMARY CANDIDATE JOE BIDEN, SAYING: "Even more important, we have to remember who we are.

This is America." Former Vice President Joe Biden made it official on Thursday, announcing his bid for the White House in a YouTube video that took square aim at the current occupant.

(SOUNDBITE) (ENGLISH) U.S. DEMOCRATIC PRESIDENTIAL PRIMARY CANDIDATE JOE BIDEN, SAYING: "If we give Donald Trump eight years in the White House, he will forever and fundamentally alter the character of this nation." President Donald Trump fired right back in his customary style, writing on Twitter, "welcome to the race Sleepy Joe.

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

It will be nasty." Soon after his announcement, a spokesman for former President Barack Obama praised Biden but stopped short of a formal endorsement.

Later on Thursday, reporters why him why.

(SOUNDBITE) (ENGLISH) U.S. DEMOCRATIC PRESIDENTIAL PRIMARY CANDIDATE JOE BIDEN, SAYING: "I asked President Obama not to endorse and he doesn't want to.

We should, whoever wins this nomination should win it on their own merits." Biden is something of a big fish in a crowded Democratic primary.

It's the 76-year-old's third bid for the party's nomination.

He made his first run in 1988, and then again in 2008.

And he enters a field full of fresher faces.

Some seemed to subtly scorn the veteran politician for his ties to deep-pocketed Democratic donors.

A statement from Senator Cory Booker's camp said, "some campaigns begin with a massive head start when it comes to fundraising... we've refused to take money from corporate PACs or federal lobbyists." A statement from Team Beto said, "today is an important day to show the strength of our grassroots campaign, especially given the fact that the former vice president has already been collecting checks from major donors." Beyond dollars, Biden may have another advantage: voters already know his name.

At this early point in the contest, that gives him an advantage in public opinion polls.

Reuters polling shows Biden leading the pack of 20 Democratic candidates.

But he faces significant challenges as well.

The party appears to have moved to the left on issues such as healthcare and the environment.

Biden is still seen by many as a centrist.

He is also facing headwinds from another direction.

Allegations recently surfaced from women about unwanted contact.

The native of Pennsylvania and seven-term senator from Delaware will be counting heavily on his long ties to the industrial Midwest, a region critics say Hillary Clinton overlooked in her failed 2016 bid and that helped propel Donald Trump to the White House.