"It is clear that President Obama wants nothing more than to talk about Governor Romney's tax returns instead of the issues that matter to voters, like putting Americans back to work, fixing the economy and reining in spending," he wrote, adding cheerily, "See you in Denver", where the two candidates will hold their first televised debate on October 3.
The exchange is the latest in a long-running saga on Mr Romney's tax affairs, which Democrat strategists believe enable them to paint the former private equity boss as a secretive elitist who used tax havens in Switzerland, Bermuda and the Cayman Islands to minimise his liabilities.
The Romney camp charges that the focus on their candidate's taxes is a distraction against Mr Obama poor record on job creation and unpopular health care reforms that are the focus of current Romney attacks over the impact on Medicare, which provides federal insurance for the retired and disabled.
However, a recent CNN/ORC poll found that two-thirds of voters believe Mr Romney should release more tax returns.
