President Trump will visit a Boeing plant in St. Louis on Wednesday to celebrate the tax cut his party handed to American companies. But lurking in the background is a clash over trade — one in which Boeing is the most vulnerable target.

The tariffs on steel and aluminum that Mr. Trump announced last week have already turned iconic American businesses — Harley-Davidson, Levi’s, makers of Kentucky bourbon — into prey for trading partners bent on retaliation.

Boeing, which sends 80 percent of its commercial planes abroad, calls itself the nation’s biggest manufacturing exporter. So it is the company with the most at stake in a trade fight — especially in China, one of the fastest-growing aircraft markets.

Singled out by the Trump administration as the nation’s primary trade adversary, China has the greatest incentive to respond to the tariffs, economists and other analysts say.