Prediction: The Trump Bull Market Is Coming to an End, and This Historically Flawless Forecasting Tool Will Be Correct, Yet Again

From a statistical standpoint, few presidents have overseen more impressive annualized stock returns during their four-year term than Donald Trump. During his first, non-consecutive term, the widely followed Dow Jones Industrial Average (DJINDICES: ^DJI), broad-based S&P 500 (SNPINDEX: ^GSPC), and growth-stock-dominant Nasdaq Composite (NASDAQINDEX: ^IXIC) soared by 57%, 70%, and 142%, respectively.

Until late February 2026, equities were enjoying an encore performance, with the Dow, S&P 500, and Nasdaq Composite all higher by a double-digit percentage since the start of Trump's second term.

But history has a way of rhyming on Wall Street. When things seem to be going too well, the rug often gets pulled out from beneath investors.

President Trump delivering remarks. Image source: Official White House Photo by Andrea Hanks, courtesy of the National Archives.

Although the Trump bull market has survived several scares, one historically flawless forecasting tool points to its end in the not-too-distant future.

Technological innovation and tax policy have fueled a bull market in stocks under Trump

Before laying the groundwork for how a multiyear rally in the Dow, S&P 500, and Nasdaq Composite will end, it's imperative to understand the backstory of why stocks have soared in the first place.

Arguably, the biggest catalyst for equities -- the advent and proliferation of artificial intelligence (AI) -- has virtually nothing to do with President Trump. Empowering software and systems with the tools to make split-second decisions without human oversight is a technological leap forward that analysts at PwC foresee creating $15.7 trillion in global economic value by 2030. Even if this estimate is only remotely in the ballpark, it signals just how massive AI hardware and applications are as an addressable opportunity.

Many of Wall Street's most influential businesses have committed tens or hundreds of billions in capital to build AI-accelerated data centers and power cloud infrastructure service platforms. Like the internet, AI is expected to lift the long-term growth trajectory of corporate America.

However, President Trump's fingerprints are etched on some aspects of Wall Street's bull market rally.

Mass buybacks are coming:

Buyback authorization announcements have risen 16% YoY so far in 2025, reaching a record $1.15 TRILLION.

This marks the 2nd consecutive yearly increase.

Since the 2020 low, share repurchase authorizations have more than TRIPLED.

Meanwhile, buybacks... pic.twitter.com/Ljfk5zTE6l

-- The Kobeissi Letter (@KobeissiLetter) October 23, 2025

For example, the passage of the president's flagship tax and spending law, the Tax Cuts and Jobs Act (TCJA), in December 2017, paved the way for public companies to alter how they reward their shareholders. The TCJA permanently lowered the peak marginal corporate income tax rate from 35% to 21% (the lowest level since 1939), thereby enabling businesses to retain more of their earnings.

While the expectation had been that higher earnings retention would lead to increases in hiring, acquisitions, and innovation, the most tangible impact of the TCJA on Wall Street has been record share buybacks by S&P 500 companies.

According to research from The Motley Fool, S&P 500 companies spent $249 billion repurchasing their stock in the third quarter of 2025 and $777 billion over the first nine months of last year. Estimates peg cumulative repurchases for S&P 500 companies at well over $1 trillion in 2025, which would be a record high.

For companies with steady or growing net income, buybacks can increase their earnings per share (EPS) and potentially lower their price-to-earnings (P/E) ratio. In other words, share repurchases can make companies more attractive to value-seeking investors.

Image source: Getty Images.

This immaculate valuation tool is foreshadowing the end of the Trump bull market

Despite several catalysts fueling this Trump-led bull market, one valuation tool has been cautioning of a disaster to come.

When most investors think about "value," they likely envision the time-tested P/E ratio. While the P/E ratio is a foundational tool for investors when quickly evaluating mature businesses, it can be easily tripped up by growth stocks and recessions. If EPS turns negative, the P/E ratio loses its usefulness.

This is where the S&P 500's Shiller P/E Ratio, also known as the Cyclically Adjusted P/E Ratio (CAPE Ratio), can come in handy. Instead of being based on trailing 12-month EPS, like the traditional P/E ratio, the Shiller P/E is based on average inflation-adjusted EPS over the trailing decade. Accounting for 10 years of EPS history ensures that shock events can't skew the readings too significantly.

Despite being introduced by economists in the late 1980s, the CAPE Ratio has been back-tested to January 1871. Over the last 155 years, it's averaged a modest multiple of 17.35.

S&P 500 Shiller PE Ratio hits 2nd highest level in history 🚨 The highest was the Dot Com Bubble 🤯 pic.twitter.com/Lx634H7xKa

-- Barchart (@Barchart) December 28, 2025

However, it's spent a majority of the last five months vacillating between 39 and 41, making this the second-priciest stock market in history. While the S&P 500's Shiller P/E isn't known for being a timing tool, history has shown that premium valuations aren't sustainable over long periods.

Over 155 years, the CAPE Ratio has exceeded 30 for at least two months during a continuous bull market on only six occasions, including the present. The five previous occurrences were all followed by significant swoons in the Dow Jones Industrial Average, S&P 500, and/or Nasdaq Composite, ranging from 20% to 89%.

Narrowing the lens even further, there are three instances, including the present, where the Shiller P/E has topped 40. Shortly after peaking at 44.19 in December 1999, the S&P 500 and Nasdaq Composite lost 49% and 78% of their respective value during the bursting of the dot-com bubble. Likewise, a Shiller P/E that crested slightly above 40 in early January 2022 gave way to a nine-month bear market that wiped away a quarter of the S&P 500's value.

The Shiller P/E Ratio has an immaculate track record of forecasting the future -- albeit not with pinpoint precision.

Coupling an expensive stock market with several other headwinds, including a divided Fed and an expected jump in inflation caused by the Iran war, provides a historically flawless recipe for the Trump bull market to end.

Sean Williams has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.