Billionaire investor Warren Buffett has campaigned alongside Democrat Hillary Clinton at a rowdy rally in his home state of Nebraska, where he challenged Republican Donald Trump to release his tax returns and said he would personally drive people to the polls in November.
Buffett said he wanted to surprise Clinton and "make a little news".
"I pledge today that on Election Day, November 8, I will take at least 10 people to the polls who would otherwise have difficulty getting there."
Buffett also said he was backing a website, Drive2Vote, that would co-ordinate transportation to cast votes and that he had reserved a trolley that seats 32 people for the same purpose.
"I'm going to be on it all day. I'm going to do selfies, whatever it takes."
Buffett said his goal was to generate the highest voter turnout in the congressional district that includes Omaha of any in the country.
Nebraska is one of just two US states that award electoral votes in presidential elections by congressional district. Buffett, whose Berkshire Hathaway conglomerate is based in Omaha, stressed that this gives power to Omaha residents to affect the outcome of the election.
Clinton responded with a promise of her own if his turnout goal is met.
"Warren and I will dance in the streets of Omaha together! Maybe if we're really lucky he'll wear his Elvis costume again!" Clinton said.
Buffett earlier challenged Trump to release his tax returns, something that presidential candidates typically do. The New York businessman has said he cannot do so until the Internal Revenue Service has completed an audit.
"I'm under audit, too, and I would be delighted to meet him any place, anytime, before the election.
"I'll bring my tax return, he can bring his tax return ... and let people ask us questions about the items that are on there," Buffett added.
He said the "final straw" for him was an ABC interview in which Trump criticised Khizr Khan and Ghazala Khan whose son died serving in Iraq.
Trump has said he was "viciously" attacked by Khizr Khan who said Trump had "sacrificed nothing", prompting Trump to say, "I think I've made a lot of sacrifices".
Buffett on Monday bluntly contradicted Trump.
"No member of the Buffett family has gone to Iraq or Afghanistan. No member of the Trump family has gone to Iraq or Afghanistan," Buffett said.
"We've both done extremely well during this period and our families haven't sacrificed anything."
