President Trump decided against announcing tariffs on steel and aluminum imports on Thursday after 18 hours of frenetic pushback from inside the White House and on Capitol Hill, two people briefed on the decision said.

Trump was scheduled to meet with steel and aluminum chief executives and announce new import restrictions, a move that would have defied Republican congressional leaders and invited retaliation by U.S. trading partners. The initial decision to proceed had been made by a tightknit group of top White House advisers while other senior officials were kept in the dark into the evening Wednesday.

But the tariff specifics proved too difficult to assemble for a Thursday announcement, forcing the extraordinary postponement only hours after Trump seemed ready to act.

The continued White House debate followed a Commerce Department finding earlier this month that rising imports of both metals threatened U.S. national security. Under a rarely used provision of U.S. trade law, the determination enables the president to limit imports through tariffs or quotas.

Chief executives from steel and aluminum companies had been invited to the White House announcement, but officials now say that meeting will be a listening session. Tariff opponents, which include the U.S. Chamber of Commerce and the Business Roundtable, hope to make the delay permanent.

“I hope this pause in the rush to impose import restrictions on steel and aluminum reflects some recognition of the kind of serious damage such measures would cause to numerous sectors of the U.S. economy and workers,” said Joshua Bolten, president of the Business Roundtable, which represents the chief executives of multinationals such as JPMorgan Chase, General Motors and Walmart.

The planned announcement had been kept secret from many senior White House officials to prevent a last-minute backlash that could sway Trump. The prospects for an announcement within 24 hours never came up at a high-level meeting at the White House on Wednesday morning, a person familiar with the meeting said. Late into the night Wednesday, White House officials and GOP congressional aides called each other seeking information about the president’s plans.

The scramble late Wednesday — when some senior administration officials were aware of the planned announcement while others were not — shows the shifting power centers within the White House economic team in recent weeks. The departure of former White House staff secretary Rob Porter, forced to resign amid allegations of spousal abuse, left the internal policy process rudderless. Other key departures also have made it easier for White House advisers with nationalist views to exert more influence.

The tariff plan followed 10 months of steady work by Ross, senior White House trade adviser Peter Navarro, and U.S. Trade Representative Robert E. Lighthizer. All three men have pushed for more protectionist policies but were opposed by White House National Economic Council Director Gary Cohn and Treasury Secretary Steven Mnuchin, who managed to delay action.

Even if Trump had made a final decision on the proposed tariffs, it would have taken days or even longer for the White House to publish details about how they would be applied because of legal requirements. Any new import limits also would have been likely to trigger immediate legal challenges by U.S. trading partners at the World Trade Organization and invite retaliation against American exports.

Sen. Roy Blunt (R-Mo.), a membership of the Republican leadership, said that he feared such tariffs would hurt companies in his home state.

“I continue to be concerned about what other countries do in response to that,” Blunt said. “In our state, we make steel and aluminum but we continue to buy a lot more than we make. Things like sheet aluminum that you use to make boats with, we make a lot of boats, it’s not available in the United States.”

The U.S. already has 169 trade taxes in place on various types of imported steel, including 29 on Chinese products. Some of the nation’s largest steelmakers, which sought the new tariffs, also are in good shape financially. Nucor Corp. reported a $1.1 billion profit last year.

“Import taxes on steel and aluminum will raise the prices of those products, which in turn will raise the price of doing business for U.S. manufacturers,” said economist Christine McDaniel of George Mason University’s Mercatus Center. “There are more people in U.S. manufacturing sectors that rely on steel then there are in the U.S. steel industry. In terms of the economics, the trade off does not make sense.”

A tariff announcement would have been seen as a further slap at China, since a top Chinese economic official is in Washington Thursday for talks aimed at forestalling a possible trade war. Liu He, one of Chinese President Xi Jinping’s closest aides, is scheduled to meet with senior administration officials in a bid to restart a direct economic dialogue that lagged last year.

The on-again, off-again tariff episode came one day after the Trump administration warned that it would vigorously defend U.S. national interests against “hostile” powers such as China and Russia, vowing to use “all available tools” to combat unfair practices.

“Countries that refuse to give us reciprocal treatment or who engage in other unfair trading practices will find that we know how to defend our interests,” said the annual report to Congress on the president’s trade agenda.

On Thursday, China’s Foreign Ministry repeated its government’s objections. “The United States is disregarding the rules of the WTO, and China is dissatisfied with this,” spokeswoman Hua Chunying told a regular news conference, referring to the World Trade Organization. She said such measures would affect employment in the United States and affect the interests of the United States’ consumers. “As for the actions of the United States, China will take proper measures to safeguard its legitimate rights and interests.”

The president’s desire for wholesale change in U.S. trade policy has met with increasing resistance from congressional Republicans as well as the business community, normally a reliable GOP ally.

Despite the president’s claims of progress, he has little to show for some of his central promises after more than a year in the White House. Though he promised to narrow the yawning U.S. trade deficit, it reached $566 billion last year, a 12.1 percent increase over 2016 and the highest mark in nine years.

The U.S. deficit with China last year hit a record $375 billion, the Commerce Department said last month.

Erica Werner contributed to this report.