Billionaire Warren Buffett ready to take on Donald Trump

Campaigning with Hillary Clinton in Nebraska Monday, Buffett savaged Trump's business record, questioning his bankruptcies and asking why the Republican presidential candidate won't release his tax returns.

The so-called "Omaha Oracle" then announced a new campaign called "Drive 2 Vote," designed to bring out voters in Nebraska's second congressional district, which offers a single Electoral College vote to the district winner.

While the state is Republican overall, President Barack Obama won a vote here in 2008 in the more liberal district where Clinton appeared Monday, which includes Omaha and the suburbs.

Buffett, who endorsed Clinton last year, was the latest in a series of business leaders attacking Trump as Clinton seeks to woo moderate and independent voters.