(Bloomberg) – Billionaire investor Warren Buffett rippedinto Republican Donald Trump Monday over his refusal to release taxreturns, his business bankruptcies, and his attack on a fallensoldier's family, repeating a famous phrase from the McCarthy era,“have you no sense of decency, sir?”

Buffett, campaigning on behalf of Democratic presidentialnominee Hillary Clinton, challenged Trump to meet him “any place,any time” with a copy of his tax returns. Buffett said he wouldbring his returns and the two of them would answer questions fromthe public. He dismissed Trump's contention that he couldn'trelease them because he's being audited. Buffett said his return isbeing examined by the Internal Revenue Service as well.

“You're only afraid if you've got something to be afraid about,”Buffett told a cheering crowd in Omaha. “He's not afraid because ofthe IRS, he's afraid because of you.”

Trump's refusal to release tax returns — which 2012 GOPnominee Mitt Romney has called “disqualifying” — would breakwith 40 years of precedent if he holds his position through theNovember election, and the issue resonates with voters. In aBloomberg Politics national poll conducted in June, two-thirds saidTrump's withholding bothered them at least a little.

Criticizing Trump's business record

The 85-year-old Buffett, known as the Oracle of Omaha, joined achorus of other Clinton backers in criticizing Trump's record as abusinessman, which is a foundation of the Republican nominee'sargument for why he should be elected. Buffett said the publiccompany that Trump set up in 1995 for his hotel, casino and resortsproperties lost money every year for a decade and investors lostabout 90 cents on every dollar. He said a monkey throwing darts atthe stock pages would have had a greater return.

Buffett said the “final straw” was the Republican presidentialnominee's swipe at the heartbroken parents of a Muslim-American warhero killed in Iraq, which has sparked condemnation across partylines.

Responding to a speech at the Democratic convention last week byKhizr Khan, who spoke about the death of his son, Army CaptainHumayun Khan, while serving in Iraq in 2004, Trump said he had“sacrificed” for the U.S. by employing “thousands and thousands ofpeople.”

Buffett said he and Trump have done very well while the sons anddaughters of other families went to serve the country in Iraq andAfghanistan. “Our families haven't sacrificed anything,” hesaid. “I ask Donald Trump, have you no sense of decency sir?”

Trump dismisses Buffett's criticism

Trump dismissed Buffett's criticism in an interview Tuesday withthe Fox Business News channel, saying Atlantic City has always been“a tough investment.”

“Well, I don't care much about Warren Buffett,” Trump said. “Ihad great timing. I got out and I made a lot of money in AtlanticCity over the years. You know, I have to look at myself, I have tolook at my company, and I made a lot of money.”

He wasn't asked about releasing his tax returns.

Clinton is campaigning in solidly Republican Nebraska withBuffett's help to burnish her credentials with the businesscommunity and to try to make the most of the state's unusual methodof apportioning its five Electoral College votes.

Economic plans

The Berkshire Hathaway Inc. chairman and chief executive officerintroduced Clinton at a Monday evening rally in Omaha that'sfocused on the Democratic nominee's economic plans. Clinton isseeking to showcase her support from prominent business leaders asshe makes a play for the votes of independents and Republicans whoare uncomfortable with the prospect of Trump in the White House.Buffett's fellow billionaire, entrepreneur Mark Cuban, endorsedClinton at a rally Saturday in Pittsburgh.

In introducing her, Buffett said he was eager to share “whatHillary can and will do in the eight years” after inauguration dayin January 2017.

Clinton ran through the outlines of her economic platform,including more spending on the nation's infrastructure, accelerateddevelopment of renewable energy sources and raising taxes on thewealthiest Americans while cutting rates for those in the middleclass.

Uneven recovery

She pledged to support the kind of small businesses “that DonaldTrump has consistently stiffed” and said that “you don't go aroundbullying small businesses just because you can.” Clinton alsoquestioned Trump's assertion that he alone can fix the country'sproblems. “I grew up in the Midwest” as the daughter of a smallbusinessman, Clinton told the crowd, saying she learned an ethic of“we'll fix it together” that Nebraskans also embrace.

She acknowledged that some parts of U.S. society haven't feltthe benefits of the recovery. “Too many people haven't gotten araise since the great crash” of 2008, she said. “There's too muchinequality and too little opportunity.” The super-rich and WallStreet will start “paying their fair share,” she said.

As Clinton and Trump head into the general election, theircampaigns are moving into a state-by-state contest to collect the270 electoral votes needed to win the presidency. Nebraska is oneof two states, along with Maine, to determine the apportioning ofits electoral votes by congressional district as well as statewide.The rest of the states and Washington D.C. are winner-take-all.

President Barack Obama is the only candidate to have managed asplit of a state's electoral vote when he narrowly won Nebraska's2nd Congressional District over Republican John McCain in2008. He wasn't able to repeat the feat in 2012. The district,which encompasses Omaha, is represented by a Democrat, BradAshford.

Buffett vows to campaign relentlessly for Clinton

Buffett vowed he would campaign relentlessly for Clinton to makesure she carries the district with a record turnout, saying he'sreserved a trolley to get people to the polls on election day.Clinton said that if he succeeds, and she wins, “Warren and I willdance in the streets of Omaha together. Maybe if we're really luckyhe'll wear his Elvis costume again.”

Buffett, who's been an Obama backer, promoted Clinton lastDecember during her primary fight against Bernie Sanders, saying inan event in Omaha that he and Clinton share a commitment to helpingthe less affluent. Buffett spoke about how incomes for thewealthiest increased seven-fold over the past two decades in theU.S. as their tax rates fell.

He was the inspiration for the so-called Buffett Rule, proposedby Obama and backed by Clinton, which would tax incomes exceeding$1 million at a minimum rate of 30 percent. Clinton, a formersecretary of state and U.S. senator, has also pledged not to raisetaxes on families making less than $250,000 a year.

Helping Clinton raise money

Buffett, an outspoken critic of the unlimited spending inpolitics that was set in motion by the Supreme Court's 2010Citizens United decision, has helped Clinton raise money but hasyet to make a major financial contribution to her presidentialcampaign. Early in the election season, he donated $25,000 to apolitical action committee that helped lay the groundwork forClinton's run for the nomination and he contributed the $2,700maximum to her primary campaign in April 2015. Last year he alsogave about $50,000 to the Democratic National Committee.

Another prominent billionaire, former New York Mayor MichaelBloomberg, also backed Clinton, endorsing her on stage at theDemocratic National Convention.

Bloomberg is the founder and majority owner of Bloomberg LP, theparent company of Bloomberg News. He was elected New York mayor asa Republican in 2001 and 2005, and to a third term as anindependent. Bloomberg was a member of the Democratic Party before2001.

Related: Here are the world's 16 insurance billionaires in2016

Copyright 2018 Bloomberg. All rightsreserved. This material may not be published, broadcast, rewritten,or redistributed.