Billionaire investor Warren Buffett ripped into Republican Donald Trump Monday over his refusal to release tax returns, his business bankruptcies, and his attack on a fallen soldier’s family, repeating a famous phrase from the McCarthy era, “have you no sense of decency, sir?”

Buffett, campaigning on behalf of Democratic presidential nominee Hillary Clinton, challenged Trump to meet him “any place, any time” with a copy of his tax returns. Buffett said he would bring his returns and the two of them would answer questions from the public. He dismissed Trump’s contention that he couldn’t release them because he’s being audited. Buffett said his return is being 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 of the IRS, he’s afraid because of you.”

Trump’s refusal to release tax returns -- which 2012 GOP nominee Mitt Romney has called “disqualifying” -- would break with 40 years of precedent if he holds his position through the November election, and the issue resonates with voters. In a Bloomberg Politics national poll conducted in June, two-thirds said Trump’s withholding bothered them at least a little.

The 85-year-old Buffett, known as the Oracle of Omaha, criticized Trump’s record as a businessman and said the “final straw” was the Republican presidential nominee’s swipe at the heartbroken parents of a Muslim-American war hero killed in Iraq, which has sparked condemnation across party lines.

Question of Sacrifice

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

Buffett said he and Trump have done very well and “we haven’t sacrificed anything.”

Clinton is campaigning in solidly Republican Nebraska with Buffett’s help to burnish her credentials with the business community and to try to make the most of the state’s unusual method of apportioning its five Electoral College votes.

The Berkshire Hathaway Inc. chairman and chief executive officer introduced Clinton at a Monday evening rally in Omaha that’s focused on the Democratic nominee’s economic plans. Clinton is seeking to showcase her support from prominent business leaders as she makes a play for the votes of independents and Republicans who are uncomfortable with the prospect of Trump in the White House. Buffett’s fellow billionaire, entrepreneur Mark Cuban, endorsed Clinton at a rally Saturday in Pittsburgh.

Clinton’s Plans

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

Clinton ran through the outlines of her economic platform, including more spending on the nation’s infrastructure, accelerated development of renewable energy sources and raising taxes on the wealthiest Americans while cutting rates for those in the middle class.

She pledged to support the kind of small businesses “that Donald Trump has consistently stiffed” and said that “you don’t go around bullying small businesses just because you can.” Clinton also questioned Trump’s assertion that he alone can fix the country’s problems. "I grew up in the Midwest" as the daughter of a small businessman, 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 felt the benefits of the recovery. “Too many people haven’t gotten a raise since the great crash” of 2008, she said. “There’s too much inequality and too little opportunity." The super-rich and Wall Street will start “paying their fair share,” she said.

As Clinton and Trump head into the general election, their campaigns are moving into a state-by-state contest to collect the 270 electoral votes needed to win the presidency. Nebraska is one of two states, along with Maine, to determine the apportioning of its 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 a split of a state’s electoral vote when he narrowly won Nebraska’s 2nd Congressional District over Republican John McCain in 2008. He wasn’t able to repeat the feat in 2012. The district, which encompasses Omaha, is represented by a Democrat, Brad Ashford.

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

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

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

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

Another prominent billionaire, former New York Mayor Michael Bloomberg, also backed Clinton, endorsing her on stage at the Democratic National Convention.

Bloomberg is the founder and majority owner of Bloomberg LP, the parent company of Bloomberg News. He was elected New York mayor as a Republican in 2001 and 2005, and to a third term as an independent. Bloomberg was a member of the Democratic Party before 2001.