LONDON — A world without nuclear weapons sounds nice, but of course that was the world that brought us World War I and World War II. If you like the sound of that, the touchy-feely “Global Zero” bandwagon is probably for you.

I’m an optimist in general but a pessimist when it comes to nations’ shifting pursuit of their interests. Humans, not states, have consciences. President Barack Obama’s commitment in his 2009 Prague speech “to seek the peace and security of a world without nuclear weapons” was a fine sentiment but a political mistake.

The idea went down well with the Norwegians, who awarded Obama a Nobel Peace Prize he should not have accepted, but overall this prospective peace blossom has wilted faster than a flower in the Scandinavian night.

(A neophyte president should question whether a peace Nobel is in any way compromising — apart from examining the merits, which were dubious.)

There were two sides to Obama’s embrace of a nuclear-free world. The first was the “vision,” as Michèle Flournoy, his under secretary for defense policy, described it recently to the Halifax International Security Forum. It was a form of utopian idealism, as Obama half-acknowledged by saying he would “perhaps” not see the end of nukes in his lifetime.

Visions are nice — Marx had one of classless societies. They can also be dangerous. Helmut Schmidt, the former German chancellor, famously remarked that people who have them should see a doctor.

The danger was that Obama, very early in his presidency, would be perceived as weak or unrealistic by rivals such as China or enemies like Iran, despite his commitment, for “as long as these weapons exist,” to “maintain a safe, secure and effective arsenal to deter any adversary.”

That perception of weakness has taken hold, reinforced by his academic-seminar approach to an Afghan surge now just seven months away from being reversed.

The second aspect of the nuclear “vision” was strategic. The idea was that it would give the United States moral leverage in persuading nations to reduce their nuclear arsenals or abandon nuclear ambitions. It would also advance U.S. nonproliferation efforts designed, among other things, to ensure no terrorists ever acquire nukes. The most dangerous aspect of the 21st-century world is the potential ability of smaller and smaller groups to do greater and greater harm.

Here the results have been mixed at best. Flournoy acknowledged that “the example that the U.S. sets probably won’t impact Iran or North Korea directly.” China continues to pursue the expansion and refinement of its nuclear arsenal. France, with its beloved “force de frappe,” was always publicly skeptical and privately contemptuous. Its recent defense accord with Britain was interesting for its inclusion of nuclear cooperation and for Prime Minister David Cameron’s statement that “we will always retain an independent nuclear deterrent.” Note the “always.”

Only with Russia was clear headway made. A new Strategic Arms Reduction Treaty signed earlier this year awaits Senate ratification. It would slash U.S. and Russian nuclear arsenals to their lowest level in a half-century. It’s compatible with America’s defense needs and should be ratified.

But the “Global Zero” idea is an unhelpful distraction because it inclines Republicans to believe Obama is not serious about maintaining and modernizing America’s nuclear arsenal. Senator Jeff Sessions, Republican of Alabama, said of the goal of a nuclear-free world: “I think it’s a dangerous concept to get into our minds — I talked with some Russians recently, and they scoffed at the idea.”

That’s a fair guide to Republican thinking; and there will be 47, not 41, Republicans in the new Senate, as well as a Tea-Party-revved Republican majority in the House. New Start’s best hope is in the lame-duck Senate. But Obama is going to have to turn the page, dump aloofness for horse-trading, airy-fairy ideals for the politics of the possible, and realize “interconnectedness” is not just the state of the world but also the way things get done in Washington.

As for nonproliferation efforts, they remain stymied by contradictions that a review conference this year did little to resolve. Three states with weapons have refused to sign the nonproliferation treaty: Israel, India and Pakistan. With all three, the United States winks at noncompliance, in the Israeli case through a secret “understanding” struck in 1969. Of course this is not lost on the likes of Iran. The case of North Korea, which renounced the nonproliferation treaty in 2003, has reinforced impressions of American inconsistency.

Perhaps Japan makes clearest why “Global Zero” is a stillborn idea. As the nation of Hiroshima, it has always pushed hard for disarmament. But as the nation facing North Korean nuclear testing and missiles, as well as an ever-stronger Chinese nuclear arsenal, it clings to the U.S. nuclear umbrella. Idealism will not keep it safe.

Obama can’t renounce “Global Zero;” that would be silly. But he should pretend he never said it. His remake for 2012 demands more of Chicago and less of Oslo. Perhaps even Benjamin Netanyahu, who has treated the president with sublime contempt since his September White House visit, would take note.