Bermuda is becoming a thorn in US presidential candidate Mitt Romney’s side as he continues to be dogged about a ‘mysterious’ offshore shell company account here as well as accounts in the Cayman Islands and Switzerland.Democrats have turned up the heat surrounding Mr Romney’s accounts, appearing on national TV talk shows, speaking to the press and launching a web ad specifically targeting the Republican’s connection to Bermuda.“Mitt Romney could be the first president in history to stash millions offshore,” said Ben Labolt, national press secretary for Obama’s re-election campaign in a web ad posted this weekend. “Bermuda doesn’t tax corporate income or capital gains — convenient.”“This is crazy, it isn’t too much to ask that a candidate for president explain why he chose to invest in other countries known as tax havens rather than the United States.”According to his opposition, Mr Romney’s family may own a shell company based in Bermuda that was transferred to a blind trust in his wife’s name right before he was sworn in as the governor of Massachusetts in 2003.Democrats are asking for Mr Romney to release his tax returns back further than two years. He is under additional pressure to disclose this information because his father, George Romney, former Michigan governor, released 12 years of his tax returns when he sought the presidency in 1968.Mr Romney’s campaign has dismissed the attacks as an “unfounded character assault”.At the end of the Mr Labolt’s web ad, he asks viewers that if they would like Mr Romney to disclose his financial information, to share the spot on Facebook and Twitter and “whatever social network is popular in the Caribbean”. So far, the ad has been viewed more than 12,500 times.Morning television talk shows have picked up on the controversy with both Romney detractors and supporters sparring over the issue and putting Bermuda in the headlines.“He’s the first and only candidate for the president of the United States with a Swiss bank account, with tax shelters, with tax avoidance schemes that involve so many foreign countries,” said Senator Dick Durbin, an Illinois Democrat, on the CBS programme, “Face the Nation” this weekend.Yesterday, campaign advisers for both President Obama and Mr Romney squared off on MSNBC’s “Morning Joe” programme trading barbs on whether Mr Romney has already disclosed enough information to clear the air.“Release the tax returns. Put all this to rest. If Mitt Romney is not hiding something in Bermuda and Switzerland and the Caymans, it will be in the tax returns,” said Obama campaign adviser Robert Gibbs.“The reason we know about these accounts, as Robert knows, is because they are in the tax returns that Mitt Romney released … we know this because he submitted this information,” Mr Romney’s adviser Dan Senor countered.The two, though, did manage to interject some humour during the face off, with Mr Gibbs jokingly adding that Bermuda is “lovely this time of year, I understand.”