US President Donald Trump warned Saturday of a massive market crash if he's not re-elected in 2020.

The President has previously warned that the economy could tank if he's removed from office.

Economists, investors, business owners, and consumers, meanwhile, worry about an economic downturn from Trump's ongoing trade wars with China and Mexico.

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United States President Donald Trump on Saturday warned without evidence of a massive market crash if he's not re-elected in 2020.

"The Trump Economy is setting records, and has a long way up to go," he said. "However, if anyone but me takes over in 2020 (I know the competition very well), there will be a Market Crash the likes of which has not been seen before! KEEP AMERICA GREAT)."

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The stock market, a close but far from perfect measure for some aspects of the economy's health, are indeed up about 27% since the President's inauguration on January 20, 2017, but those gains have been mired by massive sell offs sparked by trade war fears amid tariff fights with China, Mexico, and other countries.

Read more: Keep track of how the stock market, the US economy and other key financial indicators are performing since the inauguration of President Donald J. Trump.

Leading economists, meanwhile, are warning more trade disputes could unfurl economic gains from even before Trump's election. But even professionals struggle to forecast when — and why — economic recessions occur.

"The trade war has so far offset all benefits of fiscal stimulus and, if continued, may lead to global recession," Marko Kolanovic, JPMorgan's global head of quantitative and derivatives strategy, said on Thursday.

"If this recession materializes, historians might call it the 'Trump recession' given that it would be largely caused by the trade war initiative."

Read more: Beware a 'Trump recession': JPMorgan unloads on the president's role in erasing a full year of market progress — and lays out a scenario that could save the day

Beyond Wall Street, businesses are worried too. On Thursday, 600 companies sent a joint letter to Trump saying that broader tariffs on China would hurt workers and consumers.

Consumers share their fears too.

A closely-watched gauge of consumer sentiment fell to 97.9 at the beginning of the month from 100 in May, the University of Michigan's consumer survey indicated Friday, compared with expectations for a reading of 99.

"Consumers responded by lowering growth prospects for the national economy, and as a consequence, reduced the expected gains in employment," Richard Curtin, the survey's chief economist, said of tariffs.

Saturday's warning is far from the first time Trump has attempted to forecast an economic downturn in the event he loses the presidency.

In August 2018, he told Bloomberg News: "If I ever got impeached, I think the market would crash. I think everybody would be very poor. Because without this thinking you would see numbers that you wouldn't believe, in reverse."