As a security vacuum in Europe grows, a wider, strategic question remains unanswered: Who is responsible for keeping Europe safe and free, and at what cost?

NATO, despite being the primary framework for transatlantic military cooperation, is still an alliance of independent states that have their own budgets and priorities.

As U.S. and Russian arsenals are built down, consideration must be given to multilateral nuclear restraint.

Though leaders on both sides of the Atlantic are preoccupied with a number of current pressing issues, NATO's nuclear dilemmas cannot be put off much longer without undermining its cohesion and strength.

While NATO can extend the status quo in the short term, it cannot postpone resolving its defense and deterrence dilemmas without undermining Alliance confidence and cohesion.