A veteran investor, who has witnessed several crises over the past half-century, is worried.

“There is a lot of optimism,” said Jim Rogers, chairman of Rogers Holdings. “People are focusing on the good stuff when it comes to [Donald] Trump,” he said.

But there is no telling what Trump will do once in office and that unknown bothers Rodgers the most.

“He very much wants a trade war. And if that happens, sell everything,” Rogers told MarketWatch.

By everything, he means U.S. stocks, which rode Trump’s coattails to record levels following his November victory on euphoria over Trump’s promises to cut taxes, eliminate regulations and boost infrastructure spending.

Read:How Trump’s postelection stock market rally stacks up against other presidents

Some of that enthusiasm waned in recent weeks as doubts over Trump’s America-first agenda emerged although stocks held gains on Friday as Trump was sworn in as the 45th president of the U.S.

The Dow Jones Industrial Average DJIA, -0.17% climbed 94.85 points, or 0.5%, to 19,827.25, while the S&P 500 SPX, +0.00% 7.62 points, or 0.3%, to close at 2,271.31. and the Nasdaq Composite COMP, +0.29% gained 15.25 points, or 0.3%, to 5,555.33. All three indexes were lower for the week.

Jim Rogers

To be sure, Trump’s rhetoric has resonated with a large swath of U.S. voters who, rightly or wrongly, blame globalization for many of their woes.

“I know trade wars have always been disastrous. It leads to bankruptcies and has led to real wars,” said Rogers, speaking via telephone from his office in Singapore. “History has shown that no one has won a trade war and very few people learned the lessons of history. They ignore them because people think they are more powerful and smarter than people in the past.”

Trump swept to the Oval Office in part on antitrade rhetoric, including threats to slap China with 45% import tariffs and declare the Asian country a currency manipulator, sparking fears of escalating friction between the U.S. and its most important trading partner.

Analysts have cautioned that a confrontation between the U.S.and China could be catastrophic, likely dragging the global economy into a recession.

Read:Trump’s game of chicken with China is a lose-lose situation

The famed investor admits that there is a chance that Trump may opt to focus on the positive changes he had promised such as lower taxes and deregulation.

“If he does the good things, then happy days are here again,” he said.

The challenge for the market is that no one knows what Trump will do once he’s in office, according to Rogers who co-founded the Quantum Fund with billionaire investor George Soros, a vocal critic of President Trump.

Read:Soros says Trump ‘uncertainty’ will cause global markets to falter

Still, Rogers said there is one asset that will shine no matter which Trump shows up at the White House—the U.S. dollar.

“This is a good time to add dollars,” said Rogers, who believes that the greenback will continue to rise through this year into 2018.

The ICE dollar index DXY, -0.04% , a gauge of the greenback’s performance against a basket of six rival currencies, has risen 3% since Trump’s election.

Trump’s promise to pave the way for corporations to repatriate trillions of dollars parked abroad to avoid crippling taxes alone will ensure that the dollar remains firm even as Trump has indicated recently that the dollar may be too strong.

Read:Trump sends shiver through stock market with shot across dollar’s bow

Steven Mnuchin, Trump’s nominee to head the Treasury, on Thursday attempted to clarify that the president was referring to the short term rather than the long view. But the Mnuchin’s efforts fell short of explaining how the president will reconcile his dollar-positive policies with his desire for a weaker currency in the near term.

Also see:Trump is waving adios to the longstanding ‘strong dollar policy’

“I’m not sure Mr. Trump knows what he’s going to do, he has contradicted himself several times,” said Rogers. “He speaks loud but his words are confusing.”

The one certainty that the markets can bet on, according to Rogers, will be more chaos under Trump, which may coincide with an economic turmoil on a global scale.

“We are overdue for a crisis,” he said, reiterating his steadfast view that debt levels across the world, including in the U.S. and China, continue to swell while interest rates are at historic lows.

But that grim outlook shouldn’t scare investors away, he said.

“The Chinese have a word that opportunity and disaster are the same so when there is a catastrophe, it is also a huge opportunity,” Rogers said.