The prospect of a second term for President Trump boosted stock prices well before he was elected. Two months into his presidency, that “Trump bump” has all but disappeared.

The stock sectors that began to rally six months ago—fueled by the hope that a second Trump term could spur growth for the U.S. economy—have come falling back to earth as trade-policy whiplash and recession fears rattle markets.

Financial, industrial and small-cap stocks have erased much of the gains they logged since September, before polls showed Trump taking a narrow lead in the final weeks of the presidential race. Other trades closely linked to a Trump victory, such as bitcoin and Tesla, have slid sharply from their postelection highs.

Major stock indexes have moved in tandem. All three major stock indexes have given up their gains over the past six months. The S&P 500 entered correction territory last week—falling more than 10% from its Feb. 19 high, the quickest such slide since the start of the Covid-19 market crash. The Nasdaq Composite suffered a similar fate earlier this month.

“The market was overly optimistic about what a change in policy would mean, particularly for industrial and cyclical stocks,” said James Davolos, a portfolio manager at Horizon Kinetics. “This administration, top to bottom, is different than the first Trump administration.”

Wall Street had high hopes for the second Trump term, which many anticipated would be friendly to big business. Instead, the president has prioritized aggressive tariff policies that economists and business leaders warn will lift costs. Trump and his cabinet leaders have also tweaked, delayed or rolled back the policy multiple times, creating uncertainty about which companies and products might be most affected.

That has spooked investors, who pushed stocks even lower when the president signaled he was willing to stay the course despite the pain in the markets.

In coming days, investors are waiting for an update from the Federal Reserve, which will unveil its latest interest-rate decision Wednesday. The central bank is expected to hold rates steady, but investors will watch for signals on how Fed leaders will respond to tariffs and other economic concerns.

Trump’s first election to the presidency spurred a similar wave of bets on stronger U.S. economic growth. But eight years ago, investors mostly got what they bargained for. Major indexes marched higher in 2017, and the economy grew.

This time around, stocks have slid and preliminary estimates show gross domestic product might shrink in the first quarter.

Shares of smaller companies have been particularly hard hit. The Russell 2000 index has tumbled more than 8% this year. Individual investors have slowed their purchases of small-cap stocks: Daily retail purchases of small-cap stocks and ETFs reached more than $170 million on Dec. 2, but have been sliced in half since then, according to data from Vanda Research.

One possible explanation is the aggression—and urgency—with which the president has pursued tariffs, said Michael Green, portfolio manager and chief strategist at Simplify Asset Management.

In his first term, Trump took a more targeted approach to tariffs, singling out products like aluminum, steel or washing machines . And the duties weren’t imposed in the first few months of his presidency.

“The first Trump administration tried to load pleasure first as opposed to pain,” Green said. “This time around, they’ve reversed that process.”

To be sure, many on Wall Street agree that stock valuations were already stretched heading into 2025 and the market rally couldn’t keep up a frenetic rise indefinitely.

Others have been skeptical of the “Trump bump” from the beginning. Scott Pisarczyk in Aiken, S.C., says he generally keeps more than half his multimillion-dollar portfolio in index funds.

Despite seeing big gains during the final weeks of 2024, he moved about 15% of his holdings into stocks like Johnson & Johnson and Verizon Communications that will pay him quarterly dividends.

“I never expected it was going to last,” he said of the markets’ postelection rise. “I think for the next year, we’re going to continue to see a lot of volatility.”

Write to Hannah Erin Lang at hannaherin.lang@wsj.com