Not much rattles financial markets these days. But Michael Flynn’s guilty plea did, with stocks falling abruptly on news that President Donald Trump’s short-lived national security adviser admitted lying to the FBI, and may now provide new evidence of improprieties on Trump’s presidential campaign, and perhaps even at the White House after Trump took office.

This is the worst news Trump has received during his tenure so far, and it revives the prospect of a constitutional crisis that could involve Trump firing special prosecutor Robert Mueller. If that happens, it would be the gravest political scandal since Watergate in the early 1970s, with pressure mounting on Congress to impeach and convict the president. And if that actually happened, Vice President Mike Pence would replace Trump, becoming the 46th president of the United States.

We’re not there yet, and even if there were a move to remove Trump, he could survive it, given that fellow Republicans control both houses of Congress and a conviction in the Senate requires an imposing two-thirds vote. Still, markets are all about anticipating the future, and the prospects now include a new degree of political turmoil unprecedented even for the turbulent Trump administration.

If allegations of illegal activity involving contacts with Russian interests during the 2016 campaign get closer to Trump and his family, and Trump reacts by firing Mueller, it will undoubtedly unnerve markets. “The initial impact of that hypothetical would be a fairly significant hard stop on the psychology behind the rally we’ve seen in US equities,” says Peter Kenney, senior market strategist for Global Markets Advisory Group. “Investors have really grown to know what to expect from Trump.”

But an initial pullback might be the worst of it. The fundamental economy remains strong, and if Congress passes a big package of business tax cuts, as seems likely, that will put more wind in the economy’s sails. Meanwhile, Trump’s nominee to take over at the Federal Reserve in February, Jerome Powell, has earned plaudits from Wall Street and is a welcome successor to Janet Yellen — whom investors generally love.

Pence is more of an establishment Republican

If the drama goes as far as the removal of Trump, markets would probably find their footing quickly once the final act ended. Pence is more of an establishment Republican than Trump, and would probably calm markets once he were fully in charge.

“I don’t think anyone wants to see the country go through an impeachment trauma, but the markets could very easily live with President Mike Pence,” says Greg Valliere, chief global strategist at Horizon Investments. “Pence could perhaps get Trump’s agenda enacted more easily than Trump can get Trump’s agenda enacted. He’s well within the normal boundaries, whereas Trump is outside normal boundaries.”