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PHILADELPHIA — Vice President Joe Biden soberly warned voters Wednesday about the risks of electing Donald Trump, contending no major party nominee "has ever known less or been less prepared" to lead the United States abroad.

Biden walked on stage to the "Rocky" theme and chants of his first name before quieting applause and lowering his voice to rebuke Trump. Biden criticized the Republican presidential nominee for "exploiting our fears." He bashed Trump for trying to connect with blue collar workers, saying his reality show catchphrase "you're fired" shows his "lack of empathy and compassion."

"This guy doesn't have a clue about the middle class. Not a clue ... He has no clue about what makes America great. Actually he has no clue. Period," Biden said at the Democratic National Convention, prompting standing applause and a chant of "not a clue!"

Vice President Joe Biden delivers remarks on the third day of the Democratic National Convention at the Wells Fargo Center, July 27, 2016 in Philadelphia, Pennsylvania.
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Some in the Democratic Party would have preferred to see Biden accepting the nomination this week instead of Hillary Clinton, the woman he endorsed Wednesday. The 73-year-old Biden considered running for president but announced in October he would not after the death of his 46-year-old son Beau.

Voters have generally held a more favorable view of Biden than Clinton. Biden previously represented Delaware in the Senate and got the nickname "Middle Class Joe" for riding the Amtrak between Washington, D.C. and Delaware.

Biden spoke slowly and scanned the Wells Fargo Center as he gave thanks for the support after his son died of brain cancer last year.

"The world breaks everyone and afterward many are strong at the broken places. I've been made strong at the broken places," Biden said.

"We talk about, we think about the countless thousands of other people who've suffered so much more than we have with so much less support…but they get up."

Biden backed Clinton, calling her a "tough" and "smart" woman who has "always been there." The vice president, who has worked on health care and sexual assault prevention initiatives during his time in office, said he understands the policies Clinton is passionate about.

Biden cited her support for affordable college, expanded health care and boosting wages for workers.

"To state the obvious, and I'm not trying to be a wise guy, that's not Donald Trump's story," Biden said to laughter.

Biden added that he is more optimistic about the United States than when he was first elected to the Senate in his late 20s. He contended that America would not give into the "fear" stirred up by Trump.

Said Biden: "We do not scare easily. We never bow, we never bend, we never break."