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OMAHA, Neb. — Warren Buffett eviscerated Donald Trump before introducing Hillary Clinton at a rally here Monday afternoon, challenging him to release his tax returns and invoking McCarthyism over the Republican nominee's feud with the Khan family.

"How in the world can you stand up to a couple of parents who've lost a son and talked about sacrificing because you were building a bunch of buildings?” Buffett said before channeling Joseph Welch’s question during the 1954 McCarthy hearings.

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“I ask Donald Trump: have you no sense of decency, sir?”

The billionaire businessman also had an offer for Trump: meet anywhere, any time to show him his tax returns, which Trump has said he won’t release because he’s under audit.

Related: Trump Takes On the GOP Over Taxes—Or Does He?

"I will meet him in Omaha or Mar-a-Lago or, he can pick the place, anytime between now and election. I'll bring my return, he'll bring his return,” Buffett said to wild applause. “We’re both under audit. And believe me, nobody's going to stop us from talking about what's on those returns.

He is the third business leader to speak in support of Clinton in less than a week. Former New York City Mayor Mike Bloomberg endorsed her during an address at the Democratic National Convention in Philadelphia and famed investor Mark Cuban introduced her at a rally in Pittsburgh over the weekend.

Clinton decided to campaign in Nebraska specifically because the Cornhusker State awards electoral votes by congressional district, which could change the outcome in her favor. Buffett himself promised to take “at least ten people” who would otherwise have trouble to the polls on November 8.

The Democratic nominee, fresh off a three-day bus tour through the Rust Belt, recapped her trip for the crowd of 3,000 and slammed Trump for saying that America is “weak.” She said that the people she and her running mate, Virginia Sen. Tim Kaine, met throughout the nine-stop, 600-mile excursion “proved every day that Donald Trump is wrong.”

Clinton promised that, if elected, she will return to Omaha to “dance in the streets” with Buffett. And, “if we’re lucky,” he might even “wear his Elvis costume again!”