Why Are Elizabeth Warren and Donald Trump Trying to Weaken the Dollar?

A strong dollar makes America strong. Any campaign to devalue it is likely to backfire.

Elizabeth Warren’s “economic patriotism” differs in style and content from Donald Trump’s economic nationalism, but they have found common cause in vows to weaken the dollar. That is a strangely self-defeating agenda for patriots or nationalists of any political fashion.

Mr. Trump and Ms. Warren argue that China and other emerging rivals weaken their currencies to promote exports and gain jobs, so why shouldn’t America follow a similar policy? Here’s why: Because America is not an emerging country. It’s an unrivaled financial superpower, a position built in large part on hard-won trust in the dollar, which is an enduring source of American power and prosperity.

When the dollar strengthens and weakens in response to buying and selling in the global currency markets, foreign countries don’t protest. Occasionally they have cooperated with the United States to stabilize the dollar. But nothing will destroy trust in American financial leadership, and the benefits that go with it, more surely than for the United States government to start unilaterally manipulating the dollar for its own competitive advantage.

If Vietnam or South Korea manipulate their currencies in a bid to improve their exports, a few of their trade partners may retaliate; if the financial superpower plays the same game, the whole world will respondbecause the dollar is the international standard. A record high 60 percent of countries now measure, or “anchor,” the value of their own currencies against the dollar. Any campaign to devalue the world’s anchor could set off a destructive wave of competitive devaluations.

After World War I, when America challenged Britain as the leading global empire, the dollar began gaining on sterling as the currency that most central banks preferred to hold in reserve. Reserve currency status had long been a perk of imperial might — and an economic elixir. By generating a steady flow of customers who want to hold the currency, often in the form of government bonds, it allows the privileged country to borrow cheaply abroad and fund a lifestyle well beyond its means.

Other countries watched the United States assume this role with dismay. In the 1960s, Valéry Giscard d’Estaing, then finance minister and later president of France, called the dollar’s powerful status America’s “exorbitant privilege.” And for nearly a century now this privilege has helped to keep United States interest rates low, making it possible for Americans to buy cars and homes and, in recent decades, run large government deficits that they could not otherwise afford.