Billionaire investor Warren Buffett, pictured here at the White House United State of Women Summit in June, campaigned for Democrat Hillary Clinton in Omaha, Nebraska, on Monday. During his remarks, he challenged GOP nominee Donald Trump to release his tax returns -- a prospect the New York businessman has yet to do, he says, because of an ongoing IRS audit. File Photo by Molly Riley/UPI | License Photo
OMAHA, Aug. 1 (UPI) -- Billionaire investor Warren Buffett campaigned aggressively for Democratic presidential nominee Hillary Clinton in corn country on Monday -- and questioned Donald Trump's motives because the Republican contender still has not yet released his personal tax returns.
Speaking to Clinton supporters in Omaha Monday, Buffett championed the former first lady's vision for the United States and praised her for her campaign's transparency -- a quality he said he couldn't extend to Trump's.
"You're only afraid [to release your tax returns] if you've got something to be afraid about," he said Monday. "He is not afraid because of the IRS, he is afraid because of [voters]."
Buffett said he would meet Trump "any place, any time" with a copy of his returns.
Trump, a fellow billionaire to Buffett, has said he's not yet released the returns -- as is standard practice for American presidential nominees -- because they are being reviewed by the IRS. Buffett, though, said that explanation doesn't wash because his returns are also under IRS scrutiny.
"You will learn a whole lot more about Donald Trump if he releases his income tax return," Buffett added.
Clinton has released several years worth of tax returns and criticized Trump for his failure to do so.
Trump has said he hopes to release his returns sometime before the election.
The real estate magnate did not immediately respond to Buffett's remarks. On Twitter, however, he dedicated six separate tweets on Monday afternoon to his apparent dissatisfaction with CNN's election coverage.
"CNN will soon be the least trusted name in news if they continue to be the press shop for Hillary Clinton," one tweet said.
During his remarks, the 85-year-old Nebraska businessman also said he will lead efforts on Nov. 8 to get people to the polls by setting up ways for voters without means of transportation to get out and vote.
Clinton is campaigning in Republican-leaning Nebraska hoping to secure some of the state's electoral votes. Unlike almost all other states, Nebraska awards its five electoral votes proportionally with each congressional district. President Barack Obama took the electoral votes in Nebraska's 2nd District over Republican John McCain in 2008.
Video: ABC News