In Prague one year ago, President Obama declared “America’s commitment to seek the peace and security of a world without nuclear weapons.” The speech elicited strong reactions around the world. Elites and media who favor nuclear disarmament applauded. Others jeered, warning that a world without nuclear weapons would destabilize regional and global power balances and raise the risks of great power war.

More importantly, the range of states whose cooperation would be necessary to implement the Prague agenda either oppose it or have done little to help achieve it. Public opinion has not mobilized to make nuclear disarmament and nonproliferation a highly salient issue in any single country, including the United States. The result is a president ready to lead a long-term campaign to remove the existential threats posed by nuclear weapons, but as yet lacking sufficient followers to make it happen.

Proponents and critics have selectively interpreted or misinterpreted the vision Mr. Obama set out in Prague. Some on the left hope (and on the right fear) that he intends to pursue a treaty to ban nuclear weapons, or that he contemplates unilateral U.S. nuclear disarmament. Some believe that all of the obstacles to global disarmament will somehow fall out of the way now that the U.S. has an enlightened leader. Some charge that he will leave allies in Europe and Asia vulnerable to Russia, China, North Korea or Iran.

In reality, Mr. Obama had in mind neither the caricature of the left nor that of the right. As he said clearly in Prague, nuclear weapons probably could not be eliminated in his lifetime, and the United States would maintain a nuclear deterrent as long as other states possess or threaten to acquire these weapons. The Nuclear Posture Review released by the Pentagon on Tuesday clearly negates the idea of U.S. unilateral nuclear disarmament. So does the president’s increased budget to refurbish the aging infrastructure of nuclear weapons laboratories and material-handling facilities.

Rather, Mr. Obama posits the need for all states that now possess nuclear weapons or rely on extended nuclear deterrence to take the steps necessary to obviate their perceived need for these weapons. The Posture Review reaffirms America’s interest in a world without nuclear weapons and clearly reduces the role of nuclear weapons in U.S. security policy. It calls for high-level talks with Russia and China to promote the stability and cooperation that would lead to global reductions of nuclear weapons and cooperation in regional security-building. This is an inherently multilateral challenge. As Mr. Obama said, “all nations must come together to build a stronger, global regime.”

It is only realistic to think that the eventual elimination of all nuclear arsenals would proceed in a co-evolutionary process. Improvements in security relations among key states will facilitate arms control and disarmament steps, which in turn beget further improvements in security relations, and so on.

The new START accord helps improve U.S.-Russian relations, but differences in capabilities and doubts about intentions will make further steps harder. NATO states worry about Russian bullying and so-called “tactical nuclear weapons,” while Russia will cling to its nuclear weapons unless conventional military balances are readjusted and it is reassured about future U.S. missile defense capabilities.

The U.S. and China have only begun to explore how their strategic relations could be cooperative over the long-term. China, India, and Pakistan have not yet imagined the sorts of confidence-building and arms control processes that would be required to reverse their nuclear build ups. In the Middle East, Israel’s willingness to move toward nuclear disarmament would depend on achieving durable peace with its neighbors and verifiable guarantees that Iran and other regional states would not acquire nuclear weapons.

Countries without nuclear arms were in many ways the primary audience Mr. Obama sought to influence with the Prague speech. To some extent he succeeded. Newspapers around the world reflected wide support. The Nobel Committee was moved to award him its peace prize (which actually did not help his nuclear agenda at home or in Moscow).

But the leaders of Brazil, South Africa, Indonesia, Malaysia and other influential non-nuclear-weapon states have not embraced Mr. Obama’s logic that step-by-step progress on disarmament needs to be reciprocated by step-by-step progress in strengthening the nonproliferation regime. The Nuclear Posture Review strengthens the U.S. assurance to non-nuclear-weapon states that it “will not use or threaten to use nuclear weapons” against them. It is reasonable for such states to insist that the United States and other nuclear-armed countries must deliver more disarmament. Yet they could encourage this by communicating their intent to reciprocate with concrete measures to strengthen nonproliferation rules and enforcement in light of flaws exposed by the A.Q. Khan network and the actions of Iran and North Korea.

Two approaching events will indicate whether Mr. Obama has made progress with non-nuclear-weapon states. Next week he will be the host of a meeting of leaders from 40 states to enhance cooperation to prevent nuclear terrorism. In May, the parties to the nonproliferation treaty will gather in New York to review the accord. All the leaders attending will be asked to make commitments to guard nuclear material and prevent nuclear smuggling and terrorism. Will they follow up? Will they act to build the material-accounting and control systems necessary not only to prevent nuclear terrorism but also to enable verification of nuclear disarmament?

The nonproliferation review conference in May requires a consensus of the nearly 200 states in attendance in order to make new nonproliferation rules or to leverage compliance with current rules. In practice this makes the conference simply a barometer of moods and trends.

Will the consensus express strong enduring support for the nonproliferation regime, or instead a sense of hedging and recrimination? Will key states without nuclear weapons support universal adoption of the stronger International Atomic Energy Agency inspection protocols necessary to build everyone’s confidence that proliferation will not occur as nuclear energy technology spreads to new markets?

In word and deed Mr. Obama shows he would like to push harder to reduce nuclear dangers, which he knows cannot be accomplished with double standards and agreements that only benefit the United States. Without follow-on forces determined to widen the offensive he has opened, he risks being cut off and isolated. The most important question is whether those who support the president’s agenda will become more active or instead will turn away in passive resignation.