WASHINGTON — Not long ago, Gary Cohn was laying out an ambitious 2018 economic agenda for the Trump administration.

Fresh off the triumph of a sweeping new tax cut, President Donald Trump’s top economic aide was crafting a priority list that would touch nearly every piece of the economy. There was a $200 billion infrastructure program. There were regulations to drop. There were welfare programs to overhaul, banking rules to amend, housing finance to revamp, a new farm bill to pass.

But that was before Tuesday, when Cohn’s announced resignation heightened doubts about the direction of Trump’s economic policies just as Republican lawmakers were preparing for midterm elections against Democrats re-energized by their opposition to the White House.

Cohn’s exit followed a series of high-profile staff departures and, for him personally, a dispute with Trump over the president’s plan to impose tariffs on imported steel and aluminum. Underscoring the administration’s erratic policy process, that tariff announcement came as a surprise to many in the White House. Trump’s decision has also angered Republican lawmakers, who lobbied furiously against the move, and concerned many economists who think it could ignite a self-defeating trade war.

Cohn’s departure is likely to cause the administration to place a greater public emphasis on the president’s hard-line stance toward America’s trading partners.

With his decision to impose steep tariffs, Trump is making an aggressive play to transform a global economic system that, he argues, has exploited the United States. He campaigned in 2016 on a promise that, under his leadership, the United States would push aggressively back against existing trade pacts and eliminate the gap between what America exports and the much wider value of what it imports.