The Stock Market Stumbles After Friday's Clinton Email News. Here's Why

Shortly after news about newly discovered emails related to Hillary Clinton's private email server investigation broke on Friday, Republican strategist Patrick Ruffini noticed something:

Here's a closer look at what Ruffini is talking about. Around the time that the email news broke, the Dow Jones industrial average plummeted from a peak of 18,255 to a trough of 18,097. That's not quite 1 percent, but the sharp drop, albeit small, is a sign of a broader storyline that has persisted through this election: that investors are scared of a Trump presidency.

Justin Wolfers, economics professor at the University of Michigan and a contributor at the Upshot, has been writing about this phenomenon, noting that stock futures rose, for example, during the first presidential debate — one that (like the others) was widely perceived to be a Clinton win.

toggle caption Google Finance/Screenshot by NPR

And others have noticed it, too: Economics research firm Macroeconomic Advisors found that in recent months, "there's been an inverse correlation between the probability that Trump wins the election and stock prices," as Senior Managing Director Joel Prakken told CNBC early this month.

What's there to be afraid of? Well, for one thing, Trump always keeps people guessing. His supporters may like that, but markets don't.

"He's been unpredictable in terms of his behavior and even some of his rhetoric," said Mark Luschini, chief investment strategist for Janney. "The market dislikes uncertainty."

Trump has created plenty of uncertainty; he has flip-flopped often, and there's no telling how he will react to any given problem that comes his way.

And while it's true that Clinton would also be a new face in the White House, she is also running in large part on Obama's policies.

"Clinton is the status quo," Luschini said. "She's the known unknown, and he's the unknown unknown."

In addition, there's the little issue of Trump's tough talk on trade. U.S.-based multinationals derive a big chunk of their profits from overseas, Luschini says. In other words: Laws that make trade more difficult and costly really scare some big corporations.

That said, it's not necessarily that markets entirely dislike Trump's policies. In fact, Luschini says many investors may like Trump's policies better than Clinton's. Cutting regulations and taxes would give businesses more money to work with (and fewer restrictions on how they conduct their business) — that would make plenty of businesses happy.

On the flip side, however, there are the potential downsides to some of his policies. One widely cited study from Moody's Analytics predicted that taken together, Trump's preferred policies could create a recession. Prakken pointed to those kinds of fears as well on CNBC, noting that "some analysts suggest those policies would be quite detrimental to the economy."

The stock market has recovered some since the email news, but it's a sign of what we could see in the next 11 days — namely, more October (or November) surprises affecting not only poll numbers but maybe even inching people's 401(k)s higher or lower.