Billionaire battle: Buffett, Cuban and Bloomberg vs. Trump

Warren Buffett challenges Trump on tax returns

The race for the White House has turned into a battle between billionaires.

Berkshire Hathaway CEO Warren Buffett, Dallas Mavericks owner Mark Cuban, and former New York City Mayor Michael Bloomberg have all recently come out against Republican presidential nominee Donald Trump.

Buffett joined Democratic presidential nominee Hillary Clinton on the campaign trail Monday, and used his introductory speech to take aim at Trump and his business record.

Buffett also challenged Trump to release his taxes to the American people. "Nobody's going to arrest us, there are no rules against showing your tax returns," the Oracle of Omaha said.

The billionaire investor also criticized the New York real estate mogul's recent response to the parents of a fallen Muslim solider, asking Trump, "Have you no sense of decency, sir?"

On Saturday, Cuban endorsed Clinton and used his appearance with her to mock Trump, opening his remarks by saying "hello" to the Republican candidate in Russian.

Cuban went on to say he decided to support Clinton because Trump "scares" him.

Separately, at the Democratic National Convention, Bloomberg spoke out in favor of Clinton, calling Trump a "dangerous demagogue" who must be stopped.

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Here's how their wallets stack up. According to Forbes, Buffett is worth around $64 billion, Bloomberg is worth $48.3 billion, Trump is worth $4.5 billion (though Trump says he's worth $10 billion), and Cuban is worth $3.2 billion.

Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank," which features Mark Cuban as a judge.