Although missile defense is not at the top of the agenda as NATO leaders gather in Chicago on May 20-21, it remains an important issue for the alliance.
Despite increasingly vociferous objections from Russia, the summit will announce the next steps in European missile defense, including an "interim capability" that is being hailed as the first step toward fully protecting NATO populations from limited missile attacks.
What parts of the plan will be announced in Chicago and what happens next?
At the Chicago NATO summit, leaders will announce the completion of the first of four phases of the U.S.-led, missile-defense system in Europe.
With the first phase in place -- which involves stationing U.S. ships equipped with the Aegis ballistic missile-defense system
in the Mediterranean and working in coordination with a command center at the U.S. air base in Ramstein, Germany -- Europe will have, according to the U.S. Defense Department, "an initial capability to provide some level of defense of Europe against a threat emanating from the Middle East."
Phase 2 foresees the deployment of an Aegis system in Romania, which has already provisionally agreed to host the installation. That phase is expected to be completed by 2015.
By 2018, NATO expects to complete Phase 3, which involves a missile-interceptor base in Poland, with upgraded missiles and improved command-and-control.
The final phase is scheduled for completion in 2020 and involves the deployment of advanced interceptor missiles capable of countering not only intermediate-range missiles but also intercontinental ballistic missiles (ICBMs) that could reach the United States. The plan could also include satellite-based elements.
How much does the project cost?
It is difficult to estimate the total cost of the European missile-defense program, but estimates range up to about $9 billion. Satellite-based elements could potentially triple that figure, according to the U.S. Defense Advisory Board.
In an article published in "The Wall Street Journal" on May 14, NATO Secretary-General Anders Fogh Rasmussen emphasized that "European allies are fully involved" in the program, "supporting it politically, sharing the costs, and providing substantial assets of their own."
He noted that the Netherlands, France, and Germany have recently announced missile-defense-related programs and that Turkey, Romania, Poland, and Spain have agreed to host U.S. elements of the system.
"I expect more announcements in the months and years ahead," he added.
What are the main threats the missile-defense system will guard against?
NATO notes that more than 30 countries globally have or are in the process of acquiring ballistic-missile capabilities. The alliance argues that it must take into account this proliferation as part of its mission.
More specifically, both NATO as a whole and the United States, in particular, have identified Iran as an emerging threat. Washington says Iran will be able to threaten Europe with conventionally armed missiles by 2015. In September 2011, NATO head Rasmussen, speaking about Iran's missile capabilities, said, "The potential threat is real."
Moscow, however, sees European missile defense as a threat to its own nuclear deterrent and, as a result, plays down the threat from Iran. However, Moscow-based military analyst Pavel Felgenhauer says Moscow's position is "not so much based on real data as on a desire to present something that doesn't exist as real."
Military journalist Aleksandr Golts agrees, saying: "Russia insists that there is no danger from Iran and that American missile defense is aimed against Russia. To acknowledge a danger coming from Iran would mean destroying this entire conceptual structure."
What is Russia's position?
Moscow insists the U.S.-led European missile-defense program, particularly in its later stages involving advanced interceptors and possible space-based components, is a threat to its own strategic nuclear arsenal and a potentially destabilizing development.
NATO Deputy Secretary-General Alexander Vershbow, speaking at a recent international missile-defense conference in Moscow, noting that the Kremlin was most concerned about the later phases of the missile-defense plan, expressed the hope that intensified cooperation in the intervening years might build trust and assuage those concerns.
"We should have plenty of time to find a way to bring Russia fully into the picture to have a situation in which Russia is a full partner well before the later stages of the NATO system are operational -- the stages that Russia is most worried about," Vershbow said.
Are there prospects for cooperation with Moscow on missile defense?
Moscow argues that the only way to avoid destabilizing the current strategic order is to develop a single, jointly designed and operated missile-defense system involving Russia and NATO.
Russian Security Council Secretary Nikolai Patrushev told the same Moscow conference that Russia was even willing to help finance a joint project.
"We were prepared to go as far in this matter as the NATO side would be prepared to go, contributing to this possible joint undertaking, in addition to everything else, a substantial financial contribution as well," Patrushev said. "But there has been no interest in our proposals."
But that kind of intense missile-defense cooperation seems hard to imagine, given that much more modest cooperative efforts at U.S.-Russian missile-defense cooperation since the 1990s have floundered. In 2004, for instance, the Pentagon killed the 1997 Russian-American Observation Satellite system (RAMOS), which had failed to produce any results.
Instead, NATO is offering, as Vershbow put it, "cooperation between our respective missile-defense systems."
Vershbow told the Moscow conference, "Our vision is of two coordinated systems with one goal -- two systems that would exchange information and coordinate planning to make the defense of NATO territory and of Russian territory more effective."
Are there any other political factors at work?
Some political forces in both Russia and the West seem aimed at undermining any missile-defense cooperation.
In the United States, which will hold a presidential election in November, conservative Republicans are urging the White House to stand up to Russian President Vladimir Putin on missile defense. In a "Wall Street Journal" article on May 15, Senator Jon Kyl (Republican-Arizona) said that such defenses "are intended to defend chiefly against Iran but -- depending on future developments -- might be effective against Russian missiles as well."
In July 2011, Dmitry Rogozin -- the blunt-speaking nationalist who was then Russia's ambassador to NATO and who has since been named presidential envoy on the missile-defense issue -- met with Kyl and Senator Mark Kirk (Republican-Illinois), in Washington. "In front of me sat two monsters of the Cold War who looked at me not through pupils, but through targeting sights," Rogozin said afterward.
And Russian military journalist Golts argues that conservative forces in Moscow also benefit more from the tensions with NATO than from their resolution.
"Creating a joint-missile defense is hardly possible from the technical point of view or from the political point of view for that matter, so the NATO countries have been offering Russia various palliatives," Golts says.
"Russia, for its part, has no interest in settling the question at all. It wants to drag out the negotiations as long as possible -- which would demonstrate, as we saw at the Moscow conference, that everyone understands that Russia is a country that is capable of destroying the United States," he adds.
"And the longer they spend discussing the possibilities of Russian missiles flying to Los Angeles or San Francisco -- this is precisely the narrative that in the view of Russia's leadership enhances Russia's international authority."
Written in Prague by RFE/RL correspondent Robert Coalson on the basis of reporting from RFE/RL Russian Service correspondents Danila Galperovich and Natalya Dzhanpladova in Moscow, Aleksandr Gostev in Prague, Yevgeny Aronov in New York; and Allan Davydov in Washington. RFE/RL correspondent Rikard Jozwiak also contributed from Brussels