Mitt Romney’s campaign has made a practice of tearing down fellow Republicans in the race for the presidential nomination, but now he’s coming under heavy assault himself as president Barack Obama’s team revs up its campaign for the November election.

A major donor to Barack Obama has been accused of defrauding a businessman and impersonating a bank official, creating new headaches for the US president’s re-election campaign as it deals with the questionable history of another top supporter.