• Mark Cuban, former "Shark Tank" host and multibillionaire, mocked Donald Trump over his sweeping tariff proposals during a campaign rally for Democratic nominee Kamala Harris.
• Elon Musk, Tesla and SpaceX CEO, was set to host a talk in Pennsylvania in support of Republican nominee Donald Trump.
• Cuban is also set to appear at a Harris event in Arizona, and alongside second gentleman Doug Emhoff in Michigan.

Mark Cuban mocked Donald Trump on Thursday over his sweeping tariff proposals, suggesting the Republican presidential nominee doesn't understand his own tax ideas.

"I've learned a lot about business, including how tariffs work," the billionaire investor and former "Shark Tank" host told supporters of Democratic nominee Kamala Harris at a campaign rally in La Crosse, Wisconsin.

Trump "thinks that China pays for them," Cuban said of the proposal to hike taxes on all imported goods from China up to 60% or higher.

"This is same guy that thought that Mexico would pay for the wall," Cuban quipped, prompting laughter and cheers from the crowd.

Trump has repeatedly pointed to tariffs as a sort of cure-all, arguing that heavy import taxes — including an across-the-board tariff as high as 20% — will bring in massive revenue from overseas, fund a slew of tax cuts and boost U.S. industries, all without causing inflation.

But U.S. importers are the ones who directly pay those tariffs to the government, and mainstream economists say enacting Trump's plans would raise costs on Americans. The Peterson Institute for International Economics, for instance, found that a universal 20% tariff and a 60% tariff on China would cost the typical U.S. household more than $2,600 per year.

Cuban added that he believes Trump "used to understand how tariffs work" back in the 1990s and 2000s.

"But I don't know what happened to him," Cuban said.

The Wisconsin appearance marked the first of three swing states Cuban is visiting in support of the vice president's White House bid.

Cuban is set to head to Phoenix, Arizona, on Saturday to host a talk about Harris' economic agenda, according to the Harris campaign. On Sunday, he will campaign with second gentleman Douglas Emhoff in Grand Rapids, Michigan.

Trump is also getting a boost in on-the-ground support from a well-known billionaire: Tesla and SpaceX CEO Elon Musk.

Musk on Thursday was scheduled to embark on a multiday speaking tour across Pennsylvania with America PAC, the super political action committee he is using to spend tens of millions of dollars in support of Trump.

He was slated to host a town hall in Delaware County, Pennsylvania, on Thursday afternoon to promote absentee voting and early voting in the Commonwealth, NBC News reported.

Musk announced his get-out-the-vote plans shortly after Federal Election Commission filings revealed he gave nearly $75 million to America PAC between July and early September alone.

Musk recently joined Trump onstage at a campaign event near Butler, Pennsylvania, the same site of a July 13 rally where an alleged assassin nearly killed Trump and fatally shot another attendee.

Cuban's swing through the major battlegrounds, first reported by Yahoo Finance, follows his frequent praise of Harris on CNBC and in other media interviews.

Cuban has long been an outspoken critic of Trump. In a Harris campaign press call last month, Cuban slammed as "lunacy" Trump's promise to impose sweeping across-the-board tariffs and even higher import taxes on China.

"And so to say that we're going to tariff 10% or 20% or 60% for China or any other company, countries, that's just inflationary, and that's just the tax on the American people. That's a sales tax through and through," Cuban said on that Sept. 24 call.