Many oil and gas executives thought they had hit pay dirt with President Trump’s election. A Trump administration would be staffed by people sympathetic to the industry. More areas would be opened to drilling and costly regulations swept away.

In recent days, though, the industry has had ample reason to question that narrative.

The tariffs Mr. Trump announced on Wednesday were far steeper than many anticipated, stoking fears that an escalating trade war could curb global economic growth — or even tip the United States into a recession, dampening fuel demand.

Then, on Thursday, a producers’ cartel led by Saudi Arabia piled on, saying it was going to pump more oil than previously planned, beginning in May.

The combination shaved roughly 13 percent off Brent crude, the international benchmark, which was trading around $65 a barrel Friday afternoon, its lowest level in more than three years as stock markets reeled around the world.

The price slide is good for consumers, who benefit when gasoline and other fuels cost less. But it is spooking energy companies, particularly those in the United States, which has become the world’s largest oil producer.

If prices remain low or fall further, the industry, a major exporter and a big employer in states like Texas, could be forced to scale back investment and cut jobs.

“We’re going from ‘drill, baby, drill’ to ‘wait, baby, wait,’” said D. Kirk Edwards, chief executive of a small West Texas oil and gas producer that recently scrapped drilling plans because of higher steel costs. Steel tubing, valves and other components — which now face a 25 percent tariff — make up about 20 percent of the cost of a well, he said.

“You’re not going to go out and spend money to drill a well when your costs are higher because of steel and your product prices are dramatically lower,” Mr. Edwards said.

The fall in oil prices also highlights certain contradictions in the Trump administration’s energy goals. Mr. Trump has said he wants oil and gas companies, which backed his campaign with tens of millions of dollars in contributions, to drill a lot more wells. But he and his aides have also said they would like oil and gasoline prices to fall a lot — to as low as $50 a barrel — to keep inflation in check.

“We certainly believe it’s in the best interest of the American people and honestly the citizens of the world to have lower oil prices,” Chris Wright, the energy secretary, told reporters last month at a Houston energy conference, CERAWeek by S&P Global.

If prices keep falling, some companies will no longer be able to drill new wells profitably in certain parts of the United States, according to the Federal Reserve Bank of Dallas.

The slide was accentuated by an announcement on Thursday by eight members of the producers cartel known as OPEC Plus that they would accelerate plans for gradual production increases.

The big drop in oil prices now makes the OPEC Plus decision look almost exquisitely ill-timed. “The whole context has changed,” said Bhushan Bahree, executive director for oil at S&P Global.

Saudi Arabia, the United Arab Emirates and Kuwait had previously been fed up with overproduction by members of OPEC Plus, particularly by Kazakhstan and Iraq, that they thought threatened the group’s credibility.

“The decision was mainly about disciplining noncompliance by Kazakhstan and Iraq after months of frustration,” said Robert McNally, who was an energy adviser to President George W. Bush.

While the Trump administration wants lower oil prices, Mr. McNally said he did not think the White House pressured officials in Saudi Arabia and other countries to raise production.

Mr. McNally also said that the Saudis believe that the oil market is healthy enough that they can afford to act now.

“The long term gain to OPEC Plus discipline would be bigger than the short term pain of lower oil prices,” said Mr. McNally, who is the president of Rapidan Energy Group, a research firm.

Of course, the Saudis may have miscalculated how investors would react to the combination of Mr. Trump’s tariff and the cartel’s production announcements.

Mr. Bahree said that if the oil price plunge continues, “I am sure they are going to think about what to do.”

But it is no longer clear that Saudi Arabia and its allies would prop up prices for other oil exporters by restraining production as the country has in recent years. Oil executives “have to potentially reset expectations about the OPEC leadership’s willingness to provide perpetual price support,” Helima Croft, head of global commodities at RBC Capital Markets, an investment bank, wrote in a research note.

• This article originally appeared in The New York Times.