"If the American people want a president to add to our division, to lead with a clenched fist, closed hand, a hard heart, to demonize your opponents and spew hatred - they don't need me".
Both Biden and his wife, Dr. Jill Biden, were born in the key swing state that will be vital for any Democrat taking on Trump to win in 2020, and a Quinnipiac poll out this week indicates Biden has strong appeal among Democrats in the Keystone State.
"Some of the really smart folks say Democrats don't want to hear about unity", Biden said.
"That's what they are saying to have to do to win the Democratic nomination. Well, I don't believe it", he said. The president has already been raising money for his re-election and holding political rallies for many months.
Watch:"It goes without saying that we have got to defeat Donald Trump who, in my view, is the most unsafe president in the modern history of this country".
However Mr Biden has opened up a more than 20-point lead over his nearest rival, Senator Bernie Sanders, in several public opinion polls.
Thiessen said many Obama-Biden voters who "defected" to President Trump in 2016 are doing better under the current administration than they were during the previous eight years.
Former U.S. Vice president Joe Biden. But Biden must also balance the concern that while he is the most experienced candidate out there, he embodies the Washington insider cachet that many voters rejected in 2016 when they chose Trump over former secretary of state Hillary Clinton.
"At the core of our campaign is a simple idea: we are at our best when we're one America", Biden, who was introduced to his supporters by his spouse Jill, said.
After the vice presidency, he launched the Biden Center for Diplomacy and Global Engagement at the University of Pennsylvania in Philadelphia.
Biden has drawn criticism for his delayed entry in the race, amid concern he may not be ready to mount an energized campaign. Bernie Sanders of Vermont and Elizabeth Warren of MA also leading Trump in hypothetical head-to-head matchups, according to a recent Quinnipiac University poll. That's despite the fact that some of his own advisers worry Trump's fire will only serve to bolster Biden's standing in the crowded Democratic field.
In recent weeks, he has been criticised by Senator Kamala Harris for his past support for the 1994 crime bill that critics say led to mass incarceration of African-Americans, by Sanders for his support of the North American Free Trade Agreement, and by Senator Elizabeth Warren for his ties to the credit-card industry. Trump is correct that Obama made Biden the powerful force he is today, and to the extent that Trump was a rejection of Obama's legacy, Biden will struggle to beat Trump.