America has seen this movie before: President Trump, who imposed stiff tariffs on Monday on imported steel and aluminum, did so once before, in 2018. So domestic industries have a pretty good idea of how the story ends.

Manufacturers of trucks, appliances and construction equipment scramble to find U.S. sources of metal inputs, keeping steel and aluminum producers busier than they were before. Companies that need specific alloys that aren’t made domestically are forced to pay more. Prices rise, making end products more expensive.

But there may be plot twists along the way. Will Mr. Trump cut deals with some countries, allowing large shipments in without the new duties? Will he set up a process to give companies a reprieve if they can demonstrate a hardship? (On Monday, a White House official said there would be no exclusions.)

All of those could affect the outcome, which is why steel users are proceeding with caution. Angela Holt, who runs a precision machining company and heads the board of the Indiana Manufacturers Association, says the potential impacts on businesses are “complex.”

“It could affect not only the cost but the availability, depending on their situation,” Ms. Holt said. “It’s highly varied, even among industries — I think it’s going to depend on an individual basis where they source their materials, what the competition looks like.”

Lessons From Last Time

Although the American steel and aluminum industries are far weaker than they were in their heyday in the 1970s, U.S. companies import only about 26 percent of the steel they use, according to the International Trade Administration, and that number has been falling.