Hillary Rodham Clinton talks about the Iran nuclear agreement in Washington on Wednesday. (Carolyn Kaster/Associated Press)
Opinion writer

Dean Acheson, who is often seen as one of the great American secretaries of state, wrote in the final chapter of his memoir, “Present at the Creation,” about what he called “the struggle through illusion to policy.”

So many things that he and his colleagues had believed about geopolitics were wrong, Acheson explained. “Only slowly did it dawn upon us that the whole world structure and order that we had inherited from the 19th century was gone.”

This sense of a world turned upside down has been repeated by almost every steward of U.S. foreign policy over the past 50 years. Henry Kissinger titled his account of his tenure as secretary of state “Years of Upheaval.” The first chapter of former secretary of state George Shultz’s memoir is called “The World in Turmoil.”

This dilemma of how American power can best influence a disordered world recurs with special force now, as Barack Obama’s presidency heads toward its conclusion. Obama tried mightily to be creative in avoiding past mistakes in the use of force, as in Iraq. But he is widely judged around the world to have been a relatively weak leader — who failed to check an emboldened Russia and a rising China, and whose attempt to disentangle the United States from the Middle East yielded more problems than it solved.

As the United States is seen to recede, others advance. That’s certainly evident in the Middle East, where an array of nations that once deferred to U.S. hegemony are now acting more independently and assertively. That list of claimants to fill the perceived vacuum includes Russia, Saudi Arabia, Egypt, Turkey, Iran — even little Qatar and the United Arab Emirates. What they all share is a desire to step forward, as America steps back.

But personalizing the foreign policy challenge in terms of a supposedly weak Obama trivializes its seriousness. Many of the Republicans bidding to succeed him imply that American greatness can be restored simply by turning up the heat and displaying more willingness to use force. This “back to the future” rhetoric ignores the many ways the world has changed, which render old models of U.S. power much less relevant.

Hillary Clinton, a former secretary of state and still the leading Democratic candidate to succeed Obama, offered a thoughtful critique, as opposed to a reflexive one, in a foreign policy speech Wednesday at the Brookings Institution. Her speech was generally supportive of Obama, but she argued that he should have pursued more assertive policies toward Russia and Syria, echoing the critique she offered in her memoir, “Hard Choices.” At Brookings, she conveyed the sense that she would stick closer to the traditional lines of U.S. power, and be more forward-leaning in projecting it, than Obama has been.

Is Clinton right, that modest adjustments will restore America’s primacy? Are Republicans instead correct in urging a more radical restoration of unilateral U.S. power — by repudiating, for example, an Iran nuclear agreement that is endorsed by the world’s other leading powers? What about an alternative vision of U.S. power more attuned to the 21st-century realities that technology and communications fragment nations and alliances, and make power projection a very different challenge?

This is the foreign policy debate that the United States should be having in this campaign season. And it should be guided by Acheson’s recognition that the United States doesn’t always know the shape of the world, the balance of forces, or the way to combat rising insurgencies. What may look correct at the time can prove disastrously wrong, as in Vietnam, Iraq and the Arab Spring. Diplomats operate in a “fog of policy,” where it’s hard to see the terrain, much as warriors confront the famous “fog of war.”

When I queried a business friend about this dilemma of U.S. power, he offered a contrarian thought: What is the right “market share” for the United States in global influence? “If we had 90 percent market share in 1946, was that really better than our 30 percent, or whatever, today? For us? For the world?” Business executives have come to recognize that a globalized economy isn’t a zero-sum game; gains for China can also be gains for the United States.

The next president is going to have to steady a global system that’s gone wobbly. This need for new, creative applications of American power is not altogether different from the problems that faced Acheson, Kissinger, Shultz and others. Unfortunately, these days, we have a sterile and often dishonest debate about foreign policy. This needs to change. Perhaps Clinton’s speech this week will be a start.

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