Republicans have seized on an apparent gaffe by Joe Biden, after the US vice-president said America's middle class had "been buried in the last four years".
Biden, President Barack Obama's Democratic running mate for the presidential election, made the comments on Tuesday when speaking about the Republican camp's tax plans at a campaign event in Charlotte, North Carolina.
"How they can justify raising taxes on the middle class that's been buried in the last four years?" he asked, referring to the timeframe in which he and Obama have led the US.
Biden's remarks triggered a quick response from Obama's Republican opponent in the November election, Mitt Romney.
"Agree with Joe Biden, the middle class has been buried the last 4 years, which is why we need a change in November #CantAfford4More," Romney tweeted.
Romney's running mate Paul Ryan issued a scathing response.
"Unemployment has been above 8 per cent for 43 months. Our economy is limping along right now. Vice-President Biden, just today, said that the middle class, over the last four years, has been 'buried'. We agree.
"That means we need to stop digging by electing Mitt Romney the next president of the United States," Ryan said.
The Obama-Biden campaign said the vice-president had sought to explain that Americans had suffered because of the decisions taken by previous Republican president George W Bush.