US:DEMOCRATS begin a four-day national convention in Denver today, hoping that Barack Obama's choice of Delaware senator Joe Biden as his running mate will revitalise a campaign that has flagged in recent weeks.
With opinion polls showing the race with Republican John McCain almost neck and neck, Mr Obama and Mr Biden used their first joint appearance at the weekend to herald a sharper campaigning tone.
Mr Biden, who said last year that he thought Mr Obama was not ready to be president, told the crowd that, since then, he had learnt a lot about both candidates as he watched Mr Obama grow.
"And during those 18 months, I must tell you, frankly, I have been disappointed in my friend John McCain, who gave in to the right wing of his party and gave in to the Swift boat politics he once so deplored," he said.
Mr Obama's chief strategist, David Axelrod, said yesterday that Mr Obama had chosen Mr Biden as his running mate because he was impressed by the 65-year-old senator's wisdom.
"And not the kind of wisdom you get in Washington, DC, but the kind of wisdom you get when you overcome adversity, tragedy in your life as he has," Mr Axelrod told ABC News.
"He understands what's going on in this economy. He doesn't believe, as John McCain does, that things are fundamentally sound and we've made great progress when people are losing ground all the time." The McCain campaign yesterday released an ad suggesting that the Democratic presidential candidate passed over former rival Hillary Clinton because she "told the truth" about his lack of experience, running clips of the former first lady criticising Mr Obama.
Mrs Clinton's spokeswoman insisted yesterday that the New York senator's support of Mr Obama is clear.
"She has said repeatedly that Barack Obama and she share a commitment to changing the direction of the country, getting us out of Iraq and expanding access to healthcare. John McCain doesn't. It's interesting how those remarks didn't make it into his ad," she said.
Caroline Kennedy, a member of Mr Obama's vice-presidential vetting team, declined to say if Mrs Clinton had been screened but insisted that Mr Biden was the best choice. Introducing his running mate in Springfield on Saturday, Mr Obama stressed Mr Biden's working-class roots and his foreign policy experience.
"For decades, he has brought change to Washington, but Washington hasn't changed him," Mr Obama said.
"He's an expert on foreign policy whose heart and values are rooted firmly in the middle class." Denver authorities have prepared for violent protests this week, setting up a temporary prison in a disused warehouse and drafting in thousands of extra police. Protest groups, who are planning peaceful demonstrations throughout the Democratic convention, claim the security measures are excessive and potentially provocative.
Mr Obama said yesterday that he hopes the convention will allow him to refocus the campaign away from Republican attacks on his character and onto the economic issues that affect voters.
"I think my main goal at this convention and through my speech is to convey a sense of urgency that so many families are feeling across the country and to present a clear choice between continuing the same economic policies that have caused record foreclosures, rising unemployment, rising inflation, flat and declining incomes and wages, and a new approach to economic policies that I believe will create prosperity, growth and fairness," he told the Denver Post.
Mr Obama acknowledged, however, that adopting a more aggressive approach towards Mr McCain risked undermining his message of change based on an end to partisanship in Washington.
"It's something I worry about and wrestle with all the time. I really prefer having a debate about issues," he said.
"We're going to push back, but push back truthfully."