Campaign promises are easy. Governing is hard.

It is a truism that Donald J. Trump and his team will soon learn. And a fascinating example has emerged since the election, courtesy of global currency markets. It is a study in the kind of complex trade-offs that Mr. Trump rarely grappled with during his campaign but will face many times a day in the Oval Office.

A centerpiece of Mr. Trump’s campaign was the United States’ trade deficits. He pledged to eliminate them and create a resurgence in American manufacturing.

He has also pledged tax cuts, infrastructure spending and deregulation. That set of policies has led markets to expect speedier economic growth and thus higher interest rates in coming years. That, in turn, is driving the value of the dollar higher. Since Election Day, the dollar is up 3.6 percent against an index of six other major currencies. The value of the Mexican peso has fallen 11 percent against the dollar, a remarkable swing for the United States’ third-largest trading partner.

You don’t need to be an economist to see what that means: A pricier dollar makes it harder for American manufacturers to compete overseas; it gives an advantage to companies that locate operations elsewhere; and it will, all else being equal, tend to make the trade deficit higher rather than lower.