Democrats pressure Romney on taxes Supporters of President Barack Obama raised the temperature surrounding Mitt Romney's finances Sunday, reiterating claims that the presumptive Republican nominee used shell corporations in offshore havens to avoid paying US taxes. Democrats hope the charges will maintain pressure on the president's challenger even as the White House grapples with weak job growth. The renewed attack represents a test for the Romney camp, which came under fire from Republicans last week for being too risk adverse and potentially squandering what many believe is a strong chance to win in November's election. Mr Romney's campaign sought to focus on Mr Obama's handling of the sluggish US economy but Democrats seized on news reports that raised questions about Mr Romney's offshore holdings, pressing the Republican campaign for answers. Robert Gibbs, the president's former press secretary, went so far as to suggest that Mr Romney may have skirted the law. "The one thing he can do to clear up whether or not he's done anything illegally, whether he's shielding his income from taxes in Bermuda or Switzerland, is to do what every other presidential candidate has done and that's to release a series of years of their own tax returns," he said Sunday on CNN . The Romney campaign accused Democrats of a "disgusting" and "unfounded character assault." Earlier in the day, Kevin Madden, a senior Romney adviser, said Mr Romney "hasn't paid a penny less in taxes" even though some of his funds were domiciled in Switzerland and Bermuda. His liability is exactly the same as if he held the fund investments directly in the US. As a US citizen, he is accountable for US taxes. Some investments in some foreign countries can be tax havens, but Mitt Romney does not hold any such investments," he said. But Obama supporters said Mr Madden's comments had not made it "clear" whether Mr Romney had received tax advantages in the past. The focus on Mr Romney's personal finances is part of a broader effort to make the former private equity executive seem wealthy and out-of-touch, a perception that may have been bolstered by Mr Romney himself last week when he was photographed on a family vacation on a jet ski and a motor boat. On Sunday, the Republican nominee was due to attend three fundraisers in the Hamptons in New York, including one at the home of David Koch, the billionaire industrialist and conservative activist. The weekend fundraisers were expected to raise $3m for the Republican's presidential campaign.