During the runup to the election last fall, a vocal group of economists warned that a surprise win by Donald Trump would send financial markets into a tailspin. Instead, the opposite happened: After initially tumbling as the results came in on election night, markets surged the day after, and have risen steadily ever since.

Until today, that is. The Dow Jones Industrial Average closed down more than 120 points, making for its worst day since the election. The broader S&P 500 and the tech-focused Nasdaq Composite were down sharply as well. (Markets rebounded a bit near the end of the trading day.) To be clear, the declines stopped well short of what most investors would consider a “crash,” but they were enough that many market-watchers are predicting the end of the post-election “Trump rally.”

So what happened? Explaining market behavior is a fool’s game. But at risk of being proven a fool, let me offer a theory: Investors are waking up to the fact that they need to take Trump literally, not just seriously.

Regular FiveThirtyEight readers are already familiar with this literally/seriously construct — my colleague (er, boss) Nate Silver wrote about it over the weekend. The basic idea is that during the campaign, many in the media failed to take Trump seriously (by, among other things, doubting he could win), but insisted on taking his pronouncements literally (obsessively fact-checking his claims). His supporters, this argument goes, knew to do the opposite: They took him seriously but not literally.

Trump won the election, so the “seriously” question is no longer in doubt. But whether to take him literally was more of an open question, at least until last week, when Trump began making good on many of his campaign promises.

Here’s where the markets fit into this: My conversations with investors in the weeks since the election suggest that many of them expected Trump to govern as a fairly conventional Republican president, despite his fiery campaign rhetoric. He would cut taxes, reduce regulation and take other steps that are generally good for businesses and that are core parts of House Speaker Paul Ryan’s legislative agenda. Meanwhile, a combination of forces — Ryan’s influence, advice from Cabinet members such as Treasury Secretary nominee Steve Mnuchin, Trump’s own business savvy — would prevent Trump from making good on his less business-friendly promises, such as rolling back trade deals and restricting immigration. Sure, Trump might make life uncomfortable for the occasional outsourcing-happy auto executive, but he wouldn’t really try to roll back 20-plus years of trade liberalization.

Investors, in other words, didn’t take Trump literally.

Now, however, that confidence is looking misplaced. The details of Trump’s various executive actions are complex and ever-changing, and it’s too soon to know exactly how they will affect businesses. But Trump’s first days in office — and especially last Friday’s executive order on immigration — show that the new president isn’t afraid to carry out his most controversial campaign promises, or to create a little chaos while doing so.

That chaos has the potential to be very bad for business. Tech companies rely on immigrants — including from the predominantly Muslim countries covered by Trump’s temporary travel ban — to fill many of their most important engineering positions. Energy companies count on being able to move workers in and out of countries around the world. Manufacturers have supply chains that cross international borders. Even temporary disruptions to travel and trade could cause problems; more permanent barriers could prove disastrous.

Investors’ early confidence in Trump could still prove well-founded. The Trump administration has already backed away from the most extreme interpretation of its travel ban and from suggestions earlier last week that it would impose a steep import tax to help pay for Trump’s promised border wall. But Monday’s market jitters suggest that investors are waking up to the reality that they have to listen to all of what Trump says, not just the parts they like.