Enough with the foreign policy fairy tales

Story highlights

  • Republican presidential candidates will take part in Las Vegas on Tuesday
  • Aaron Miller: Candidates in both parties should avoid making unrealistic promises on foreign policy

Aaron David Miller is a vice president and distinguished scholar at the Woodrow Wilson International Center for Scholars and author of "The End of Greatness: Why America Can't Have (and Doesn't Want) Another Great President." Miller was a Middle East negotiator in Democratic and Republican administrations. Follow him on Twitter @aarondmiller2. The opinions expressed in this commentary are his.

(CNN)On Tuesday night, when nine hopefuls take the stage in Las Vegas for the main Republican presidential candidate debate, nowhere will the differences between President Obama and that field appear sharper than on foreign policy.

From the Islamic State of Iraq and Syria (ISIS) to Syria itself to dealing with Iran and Vladimir Putin, Americans will hear promises of a transformation in how the next president will lead the nation abroad: President Barack Obama's risk aversion will be replaced by risk-readiness and his weakness by strength and resolve and America's rightful place in the world -- as leader not follower -- will be restored. In short, we will all live happily ever after.
Don't count on it.
    Aaron David Miller
    Having participated in my fair share of presidential transitions, I'd bet against this fairy tale foreign policy and wager on more continuity than change. And that goes for Democratic candidates too. Because the reality is that the next president will face a cruel and unforgiving world, bad options, hopeless causes abroad, and existing commitments not so easy to change.

    Undo Obama commitments?

    Not so Fast. Several Republicans, including two of the leading candidates, Ted Cruz and Marco Rubio, have threatened to literally shred the Iran nuclear deal or expressed hope that it will be reversed.
    But if either of them does win the White House, we'll be around a year into implementation of the nuclear accord. So unless Iran cheats big time, (and it's not clear why they would -- this is one good deal for them) it won't be easy or even desirable for the next president to take such a step. Indeed, even Republican frontrunner Donald Trump has said it's too hard to ditch the deal, saying instead he'd would work to "police" Iran to make sure it lives up to its terms.
    No president wants or needs a foreign policy crisis with allies or adversaries during the first 100 days of his/her administration. So, slowing down normalization with Cuba? Sure. Ratcheting up the rhetoric against Iran, the Paris Climate Change agreement and Russia's president? OK. But undoing or withdrawing from commitments will be much harder the more time passes.

    Talk is cheap

    Nowhere will the gap be greater between what the Republican candidates say they will do and what they will be able to do than on Syria and the war against the jihadis.
    But talk is cheap, and the war against ISIS and the jihadis will be a long one. If any of the tough talking Republican hopefuls become president, they will discover that winning that war isn't so simple. Campaigning on U.S. leadership is one thing. Combatting terrorists and finding long-term solutions in the face of the meltdown in Syria and Iraq, uncooperative allies, and the limits and complexities of no-fly zones and large deployments of U.S. ground forces is quite another.
    The same is true for dealing with Putin in Syria or Ukraine and Iran. These actors have leverage, will and have demonstrated they can act on familiar terrain. From what to do about Syria, Iraq, the Islamic State, or Putin's adventurism, a Republican president, or even a Democrat who aspires to be tougher or bolder than Obama, will be hard pressed to find much better -- let alone heroic -- solutions to any of these problems.

    Things really have changed

    Republicans are right to assert that America must lead. But their conception of leadership needs to be geared to the realities of both the past and present.
    The notion that America once dominated the world with bold and heroic leadership isn't a myth so much as it is a legacy limited to discrete periods of the past century. During World War II and the post-war years, the United States played an extraordinary role in Europe and Japan, as it did in the early 1970s in its diplomacy with China and détente with the former Soviet Union. It also helped to bring about the end of the Cold War under Ronald Reagan and George H. W. Bush. And there was the first Gulf War, and the reunification of Germany, too.
    The United States played a leading role in all of this. But it is important to remember that these periods were all marked by failures and stumbles too, including two costly land wars in Asia, CIA support for failed revolutions, expensive coups and authoritarian regimes. And the last time a Republican president led the nation, we ended up in a disastrous war in Iraq in which the returns have been buried by the tragic costs.
    So while the United States is likely to remain the world's most consequential power -- one with a better balance of political, military, economic, and soft power than any other nation -- it is unclear whether it will be able to play the vaunted role of the world's only truly indispensable superpower. In fact, what that term even means in view of today's many and complex global challenges isn't at all clear.
    Forget heroic diplomacy and saving the world. Governing -- not campaigning -- is about choosing, setting priorities, and identifying what's vital from what's discretionary, what's doable from what's not, and sorting through options that more often than not are those that run somewhere between bad and worse. And above all, it is about making sure that when presidents say things, they follow through. If there is a simple definition of the vaunted term U.S. credibility, it must certainly include saying what you mean, meaning what you say and if you have a red line, being prepared to back it up.
    Right now, instead of spending time making promises they may well not be able to keep, our presidential candidates -- Republicans and Democrats alike -- ought to be thinking about what they plan to do should they actually get the job. And chances are their collective major challenge will be less a matter of grandiose strategies and heroic acts and more about figuring out how they're going to find a better balance between George W. Bush's risk readiness and Barack Obama's risk aversion.
    Ultimately, one thing is clear: Protecting U.S. interests in a cruel and unforgiving world will require not only bold leadership, but prudence and wisdom too. Let's hope we get more of that than fairytale foreign policy from our candidates.