The stock market’s post-election bifurcation sharpened Monday as technology shares extended their worst performance since the start of the bull market on speculation Donald Trump’s trade and immigration policies will translate into lower earnings.

Apple Inc., Facebook Inc. and Alphabet Inc. led the S&P 500 Information Technology Index down 1.7 percent for the biggest retreat since September. The group stands out as the only industry that normally benefits from a rising economy not to rally on speculation Trump’s policies will stoke domestic growth. Tech stocks in the benchmark equity gauge have slumped 3.1 percent over four days, trailing the S&P 500 Index by 4.2 percentage points, the most since May 2009. Small caps in the Russell 2000 Index surged 1.2 percent to an all-time high.

No single fact explains the tech rout though everything from trade and immigration policy to industry rotation to flat-out campaign retaliation have been cited. Technology is the biggest group in the S&P 500 by far and one of the only ones to consistently post earnings growth over the last 18 months.

“Technology provides the productivity gains for the global economy and many of the large-cap names like Apple and Amazon were carrying the torch for the market,” Channing Smith, a managing director at Capital Advisors Inc. in Tulsa, Oklahoma, said by phone. The firm oversees about $1.8 billion. “Without their participating, that’s definitely going to create a headwind for the market.”

The S&P 500 slipped less than one point for a second day of losses, with tech giants bearing the worst of the rout. The FANG block of Facebook, Amazon.com Inc., Netflix Inc. and Google parent Alphabet each fell more than 2.4 percent. The group has dropped every day since Trump’s victory, sinking 8 percent for the worst retreat since February amid concern about the impact of Trump’s policies on trade overseas, where U.S. technology companies thrive.

The industry, which largely supported Hillary Clinton during her presidential campaign, may also face higher hurdles for expanding their footprints after some high-profile business leaders including Amazon Chief Executive Officer Jeff Bezos clashed with Trump during the election. Trump, responding to negative coverage in the Washington Post, which is owned by Bezos, maintained Bezos purchased the news organization to gain political influence and avoid antitrust scrutiny. Shares of the online retailer have lost more than $30 billion in value since Tuesday’s vote.

“It’s a big deal with what potentially Trump could do,” said Blake Harper, an analyst that covers internet stocks at Loop Capital Markets LLC in Chicago. “If you look at investors in Alphabet, Facebook and Amazon, they’re stacking some type of operationality for them to continue to expand internationally and also expand into other different categories outside their core markets,” he said. “He definitely indicated he would pursue antitrust measures against companies like Amazon. You’d have more restrictive policies to prohibit expansion.”

Any slowdown in tech earnings may deal a blow to a market that just emerged from a five-quarter profit slump, the longest since the global financial crisis. While S&P 500 income rose 2.7 percent in the third quarter, profit at tech firms expanded almost 8 percent, actual results and analyst estimates compiled by Bloomberg show.

The decline in tech shares came after they extended their leadership at the fastest rate in four years, raising their representation in the S&P 500 by more than 1 percentage point to a 15-year high of 21.4 percent in the third quarter. From Apple to Facebook, mega techs now occupy half of the top 10 spots in ranks of the most valuable American companies, matching the number at the peak of internet mania.

For now, the market seems to be holding up, with S&P 500 trading within 1.2 percent of an all-time high, as the retreat in tech stocks has been countered by rallies in financial and industrial companies, shares expected to benefit from Trump’s plans to boost fiscal spending and ease regulations. Banks climbed 2.3 percent Monday, extending their gains since Trump’s victory to 11 percent, while industrial stocks have added 5.2 percent in that time.

“The market is getting ahead of itself here and selling off and being hard on tech,” said Timothy Ghriskey, who helps manage $1.5 billion as chief investment officer at Solaris Asset Management LLC in New York. “Tech is where a lot of gains were, so as money gets shifted around to different sectors, meaning into financials and into health care and industrials, it has to come out of somewhere and a lot of it has come out of tech.”