Sustained attacks by President Barack Obama's campaign on Republican rival Mitt Romney's business history and refusal to release more tax records appear to be working. More than a third of voters who are registered to a party or as an independent said they had heard about Romney's taxes and his time at Bain Capital private equity firm. They also said that this had given them a less favorable impression of the Republican candidate. Particularly worrying for Romney is that a large slice of independent voters are also buying into the Obama campaign's portrayal of him as a ruthless businessman who may be hiding something in his taxes.