A weak US dollar isn't a good thing for stocks, if history is any guide. 

The US dollar touched a three-year low on Monday as President Trump ramped up his attacks on Federal Reserve Chair Jerome Powell. 

The US Dollar Index (DX-Y.NYB) has declined 9% year to date.

In a new note on Monday, Trivariate Research founder and former Morgan Stanley chief US strategist Adam Parker went back to 2001 to see how dollar weakness has impacted markets. Parker identified 16 periods where the US dollar weakened at least 5%. 

Some of his findings:

• The median performance of the US equity market is 7.5% during a period of dollar weakness, which is the sixth worst of the 55 regions Parker and his team evaluated. The top three countries in terms of median performance: Greece (+17.6%), Indonesia (+17.5%), and Peru (+16.4%). 

• Malaysia, South Africa, and Portugal are markets that have been up in absolute terms in all 16 prior periods when the dollar weakened.

• Only Mexico, Israel, Sri Lanka, and Pakistan have average stock market performance worse than the US when the dollar is materially weakening against the DXY. 

• The worst performances by country during the latest bout of dollar weakness include Indonesia (-11%), Denmark (-12.1%), and Taiwan (-13.4%). 

• The best performances by country during the latest bout of dollar weakness include Spain (+27.3%), Poland (+30.7%), and Colombia (+32.9%).

• On average, Metals & Mining, Consumer Finance, and Transportation Infrastructure were the best-performing sectors in the 16 periods of dollar weakness going back to 2001. Biotechnology, Banks, and Healthcare Technology were the worst.

"There is no question in our minds that the performance within the US equity market during the recent period of dollar weakening is far different for very understandable reasons than the previous regimes where the dollar weakened by at least 5% against the DXY. Hence, we can't say with confidence that just because something has not happened in the past it can't happen this year," Parker said.

The US market's performance this month has generally vibed with the historical trends.

The S&P 500 (ES=F) and Nasdaq Composite (^IXIC) are down about 4% each in April, with the Dow Jones Industrial Average (^DJI) off by 5.6%. Market leader Apple (AAPL) has dropped 8.5%. 

Gold prices have climbed to a record high. 

Year to date, the three major indexes are down more than 7%, with the Nasdaq leading stocks lower with a 10% decline.

Investors continue to take their cue from the Trump administration's scattered approach to tariffs. More recently, concerns about the impact of tariffs on corporate profits and the economy have been compounded with fresh fears about Federal Reserve independence. 

President Trump has taken to social media and the airwaves to threaten the firing of Fed Chair Jerome Powell.

Powell's term runs until May 2026, so any attempt by the administration to remove Powell would be unlikely to be well received by global markets. 

"The U.S. economy remains remarkably resilient and could yet escape its current problems without slipping into recession. However, resilience is not the same thing as exceptionalism and investors need to consider whether a continued gradual deterioration in U.S. economic performance warrants both a more cautious stance overall and a broader diversification into international assets," said JPMorgan Asset Management chief global strategist David Kelly in a note on Monday.

Brian Sozzi is Yahoo Finance's Executive Editor. Follow Sozzi on X @BrianSozzi, Instagram, and LinkedIn. Tips on stories? Email brian.sozzi@yahoofinance.com.

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