President Trump on Tuesday. (Leah Millis/Reuters)

Regarding the March 9 editorial “No way to treat a friend”:

Through the economics lens, what President Trump has done and is doing now is testing the “rent” of American credit on the diplomatic stage. “Rent” in economics means the discrepancy between what you pay now and the highest you want to pay for the same thing.

In Mr. Trump’s eyes, U.S. allies would be willing to pay much more for what the United States is providing for the global order, so he wants to rebalance the status quo and rebuild a new equilibrium on the global stage. The real crisis will come when the push by Mr. Trump hits our allies’ warning lines.

This is only the second year of the Trump administration. We need to worry about the frequency, degree and extent of intimidating moves in the future. Breaking down the former equilibrium is easy, but building up a new one is much harder, especially if Mr. Trump is so variable.

Shuai Tang, Arlington