Trump is going after Amazon; Congress is after Facebook; Google is too big, and Apple is short of new products. Is it any surprise that sentiment toward the tech industry giants is turning sour? The consequences of such a readjustment, however, may be dire.

The past two weeks have been difficult for the tech sector by every measure. Tech stocks have largely driven the year’s stock market decline, the largest quarterly drop since 2015.

Facebook saw more than $50bn shaved off its value after the Observer revealed that Cambridge Analytica had harvested millions of people’s user data for political profiling. Now users are deleting accounts, and regulators may seek to limit how the company monetizes data, threatening Facebook’s business model.

On Monday, the Federal Trade Commission confirmed it was investigating the company’s data practices. Additionally, Facebook said it would send a top executive to London to appear in front of UK lawmakers, but it would not send the chief executive, Mark Zuckerberg, who is increasingly seen as isolated and aloof.

Shares of Facebook have declined more than 17% from the close on Friday 16 March to the close on Thursday before the Easter break.

Amazon, meanwhile, long the target of President Trump’s ire, saw more than $30bn, or 5%, shaved off its $693bn market capitalization after it was reported that the president was “obsessed” with the company and that he “wondered aloud if there may be any way to go after Amazon with antitrust or competition law”.

Shares of Apple, and Google’s parent company Alphabet, are also down, dropping on concerns that tech firms now face tighter regulation across the board.

For Apple, there’s an additional concern that following poor sales of its $1,000 iPhone X. For Google, there’s the prospect not only of tighter regulation on how it sells user date to advertisers, but also the fear of losing an important Android software patent case with the Oracle.

Big tech’s critics may be forgiven a moment of schadenfreude. But for shareholders and pension plans, the tarnishing of tech could have serious consequences.

Apple, Amazon and Alphabet make up 10% of the S&P 500 with a combined market capitalization market cap of $2.3tn. Add Microsoft and Facebook, with a combined market value of $1.1tn, and the big five make up 15% of the index.

Overall, technology makes up 25% of the S&P. If tech pops, the thinking goes, so pops the market.

“We’re one week into a sell-off after a multi-year run-up,” says Eric Kuby of North Star Investment Management. “The big picture is that over the past five years a group of mega cap tech stocks like Nvidia, Netflix, Facebook have gone up anywhere from 260% to 1,800%.”

Until recently, investors have been betting on years of unfettered growth. In a tighter, more regulated environment that bet may not look so good.

“Most growth investors were not looking at companies’ cash flow for the basis of the stock price. They were looking at momentum, but if you look at Facebook it’s still trading at 30 times trailing earnings. These stocks have been largely detached from any earnings analysis so there’s room for more downside pain,” said Kuby.

Daniel Ives at GBH Insights wrote in an investors’ letter that the “last thing nervous tech investors wanted to see … was news that Trump is targeting Bezos and Amazon over the coming months”.

The momentum of that collision seemed to build on Thursday after Trump amplified his anti-Amazon comments, alleging it shortchanges taxpayers. Trump also attacked its use of the US Postal Service and its impact on traditional retailers.

“I have stated my concerns with Amazon long before the election,” he wrote on Twitter. “Unlike others, they pay little or no taxes to state & local governments, use our postal system as their delivery boy (causing tremendous loss to the US), and are putting many thousands of retailers out of business!”

The president’s commentary was followed by an ominous tweet from his campaign manager, Brad Pascale.

“Do not forget to mention that Amazon has probably 10x the data on every American that Facebook does. All that data and own a political newspaper, The Washington Post. Hmm …”

Kevin Hassett, a White House adviser, later told Fox Business News: “The general principle that I know deeply concerns the president is that we need to live in a world where the government sets a level playing field between internet vendors and mom-and-pop stores.”

For a president who frequently touts stock market highs as a totem of his success as head of the executive branch, the attack on tech appears counterproductive. “Any political question is very confusing because you can’t tell what’s the issue of the day and what’s a real issue. The Facebook political issue is clearly one they’re going to have to work their way through. Amazon is harder to handicap,” says Northstar’s Kuby.

For now, analysts seem unfazed. On Thursday, investors seemed to shrug off Trump’s attack. Deutsche Bank analyst Lloyd Walmsley said: “We do not think attacking Amazon will be popular.”

But if companies like Amazon and Facebook – data companies at their core – are forced to change the way they do business, earnings estimates will have to drop and stock markets will go with them, says Kuby.

“Their earnings have only ever gone one way, which is up. Once they start coming down, the multiples come down, and we’re going to see even bigger pressures on the stock. There’s significant chance that their business are going to be affected.”