Earlier this month in Warsaw, President Obama proposed a $1 billion "European Reassurance Initiative" to support NATO allies in Central and Eastern Europe in response to Russian actions in Ukraine. The new money would support additional exercises and troop rotations in Eastern Europe; additional U.S. naval deployments in the Black and Baltic seas, and steps to build the capacity of Ukraine, Georgia and Moldova so they can work with NATO and provide for their own defense.

A step in the right direction? Yes. But if Russian actions in Ukraine are truly a game-changer in Euro-Atlantic security, $1 billion over the next year isn't going to change the game. In order to successfully navigate the current crisis, prevent the next, and build a foundation for a safer and more stable Europe, Washington and its NATO allies must think and act more boldly on both defense and diplomacy.

On the defense side of the ledger, one thing is clear: More resources from Washington — and NATO — will be required. A reasonable guess would be up to another $1 billion per year for the next five years just to sustain a "persistent U.S. air, land and sea presence in the region," as promised in Warsaw. Additional funds will be needed if the United States follows through on prepositioning of equipment in Europe, improvements in NATO infrastructure and changes in America's European force posture.

Against this backdrop, the White House's assurance that this new money "will not come at the expense of other defense priorities, such as our commitment to the Asia Pacific rebalance" may be true for this year, but it cannot — nor should it — be the foundation for a durable new commitment.

So where will the United States and NATO find the money? The most sensible answer is for Washington and its NATO allies to move now to reduce the staggering costs associated with a planned $13 billion modernization of the U.S. B61 nuclear bomb now stored in European bunkers and to decisively change the nuclear component of NATO's defense posture.

During a briefing in 2010, the vice chairman of the U.S. Joint Chiefs of Staff, Gen. James E. Cartwright, stated that the B61 in Europe did not serve a military function not already addressed by U.S. strategic and conventional forces. The Ukraine crisis — and Obama's Warsaw initiative — underlines that the most effective and reassuring NATO deterrent going forward is investments in conventional capabilities relevant to the threats NATO faces today. American tactical nuclear bombs that provide no modicum of deterrence beyond that already provided by the strategic nuclear forces of the United States, Britain and France are a heavy weight around NATO's neck.

Ironically, it is the new NATO allies — often perceived as stumbling blocks to this long-overdue change in NATO's nuclear posture — who should now be going to the NATO summit in September saying, "Let's stop spending on redundant nuclear capabilities; let's use those resources over the next five years to sustain and expand the European Reassurance Initiative." They should also follow Poland's lead and commit to increasing their own defense spending to 2 percent of gross domestic product, the official NATO standard.

A game-changing response to the Ukraine crisis must include more than new defense muscle. NATO should use the September summit to begin outlining the contours of a new security strategy for the Euro-Atlantic region — one that goes beyond simply reassuring NATO. The objective would be for Washington and its NATO allies to work with Moscow toward building mutual security in the Euro-Atlantic region, through a new political and military dialogue mandated by the highest political levels, where security can be discussed comprehensively and practical steps can be taken on a broad range of security issues.

Realistically, a new dialogue mandated by political leaders may be difficult to launch until the Ukraine crisis stabilizes — which may still take months. But that should not preclude NATO from uniting behind a new strategy for Euro-Atlantic security in September. Indeed, without a new strategy — and new diplomacy with Moscow in this difficult period — Washington's effort to reassure NATO in isolation risks contributing to another generation of East-West conflict.

On the beaches of Normandy, European leaders and veterans commemorated the historic invasion that began a new chapter in world history. From June 6, 1944, the defeat of Nazi Germany took only one year. That herculean task required an unprecedented level of commitment, cooperation and innovation between the United States and its European allies, including Russia. The Cold War that followed was not inevitable; neither is a new Cold War today. But the combined efforts necessary to avoid that outcome — in both defense and diplomacy — are not yet evident.

Steve Andreasen, the director for defense policy and arms control on the White House National Security Council staff from 1993 to 2001, is a consultant to the Nuclear Threat Initiative in Washington, D.C., and teaches at the University of Minnesota's Humphrey School of Public Affairs. He is a member of the International Institute for Strategic Studies.