US President Barack Obama released his tax return on Friday, showing that he earned nearly $800,000 last year, leveraging the annual rite to launch a new attack on his wealthy Republican foe Mitt Romney.Cranking up their campaign for a second term ahead of November's election, Obama and Vice President Joe Biden have now made their tax returns public for each year going back to 2000. They complain that Mr Romney, a multi-millionaire venture capitalist they are trying to portray as oblivious to the economic struggles of middle class American families, has not done the same. Mitt Romney has released his return for 2010 and an estimate of his taxes for 2011, but has yet to do the same for previous years, including when he worked at the investment firm he founded, Bain Capital. In 2010, Mr Romney paid a lower tax rate than many middle class Americans -13.9 per cent on income of $21.7 million. His estimated income from 2011 was $20.9 million and his fortune is esti...