THE BURNED OVER DISTRICT

That the various financial markets that would be affected by a shutdown have no guidelines to judge the degree of danger from the Pumpkin Potemkin. And because of this, he has already roiled the markets to a greater extent than previous political showdowns.

In recent years, government shutdowns have become so common that markets have either embraced them or shrugged them off. But as investors absorb the possibility of a closure this fall, market tremors are likely to intensify, experts say. The past will not necessarily be prologue this time around.

That’s the view of Isaac Boltansky, director of policy research at Compass Point Research & Trading in Washington. Noting that during the past three shutdowns, the stock market was unfazed by the political gamesmanship, Mr. Boltansky said, “I think this time will be worse because of the uncertainty from President Trump.”

Investors are grappling with two matters right now: the need to raise the nation’s debt ceiling in September so the government can pay its obligations, and the desire to have a federal budget in place by Oct. 1 to avoid a shutdown.

Earlier this week, Treasury Secretary Steven Mnuchin tried to reassure investors on the first matter. “We’re going to get the debt ceiling passed,” Mr. Mnuchin vowed at an event in Louisville, Ky., on Monday. He also predicted that the ceiling would be raised cleanly — that is, without spending reforms attached to the increase that are intended to move the government toward a balanced budget.

But the next day Mr. Trump invoked the government shutdown, spooking Treasury investors. Faced with the possibility of problems with both the debt ceiling and a shutdown, investors holding T-bills maturing in early October began selling. Short-term Treasury investors, like the institutions that oversee money market funds, can’t afford to wait around to see if they’ll be paid on time. It’s easier to bail out of the holdings that could be affected.

Stocks also weakened on the prospect of a shutdown — a very different investor response than has been seen during recent government closures.

Mr. Boltansky looked back at the stock market’s performance during all 18 government shutdowns, starting in 1976. He found that the Standard & Poor’s 500-stock index averaged just a 0.6 percent loss over the course of those closures.

Early on in shutdown history, investors reacted very negatively. Closures in 1976 and 1977 coincided with 3 percent declines in the S. & P. 500.

As investors grew more accustomed to shutdowns, they seemed to become more blasé about them. During the mid-1990s and the 2013 closure, for instance, stocks actually rose. They gained 3.1 percent during the 2013 stoppage.

Although stocks rose on Friday, investors should not expect such a performance this time, Mr. Boltansky said. One reason is that a government closure would raise serious doubts about the ability of the Republicans in Congress to get anything done.

“It will confirm one of the market’s fears that the Republicans are not a political party but a government coalition made up of leadership loyalists, conservatives and moderates,” Mr. Boltansky said. “If you have that dynamic, how can you get anything done legislatively?”

Yes, the Republicans Party's legendary prowess at failing to govern has added extra spice to the pending craziness. Best to buy your popcorn now while your money has some value.