Philadelphia - Levelling a blistering attack on Donald Trump, US Vice President Joe Biden put on his rhetorical hat as "middle-class Joe" on Wednesday and told Democratic delegates and millions of television viewers that the billionaire businessman "has no clue" about the needs of working-class people or what makes the nation great."He's trying to tell us he cares about the middle class?" Biden said at the Democratic National Convention. "Give me a break. That's a bunch of malarkey."The delegates ate it up, chanting "not a clue, not a clue" and jumping to their feet over and over, waving signs that read simply "Joe".It was a bittersweet moment for Biden in more ways than one. He took note of the loss of his son, Beau, to brain cancer a little more than a year ago. And left unspoken was the knowledge that Biden had long hoped for a very different kind of convention moment — one in which he claimed the nomination for himself.Biden, 73, ran for president twice and spent months last year debating whether to challenge Hillary Clinton for the 2016 nomination before he opted out in October.'There's only one person in this race' But Biden put that behind him and delivered a stirring defence of Clinton as smart, tough and passionate about helping others."There's only one person in this race, who will be there, who's always been there for you," he declared.Then he quickly segued into a harsh comparison with Trump, taking note of his own nickname as "middle-class Joe.""To state the obvious — and I'm not trying to be a wise guy here — that's not Donald Trump's story," Biden said."His cynicism is unbounded," Biden said, citing a lack of empathy and compassion summed up in Trump's signature catchphrase, "You're fired".The vice president gave Trump one distinction: "No major-party nominee in the history of this nation has ever known less or has been less prepared to deal with our national security."We cannot elect a man who exploits our fears of ISIS and other terrorists, has no plan whatsoever to make us safer, a man who embraces the tactics of our enemies — torture, religious intolerance," Biden said. "That's not who we are. It betrays our values."Political careerBiden was introduced by his wife, Jill, and with a six-minute video that summed up his four-decades-plus political career as a congressman, senator and vice president."He was authentic long before it became a buzzword in politics," his wife told the delegates, who showed they agreed, some waving signs that read "Scranton," his working-class hometown in Pennsylvania."I love Joe Biden," said Tammie Lewis, a Michigan delegate. "He should have been our next president.""He's always come across as just one of us," she added.First lady Michelle Obama, who got a shout-out from Biden in his speech, tweeted back: "To one of my favorite men in the world. Joe, thank you & Jill for all you've done for this country."Biden's speech to the convention is likely one of the last major addresses of his political career. He has said he expects to stay involved on issues after his tenure as vice president ends but he has no plans to run for office again.