When all is said and done—or, rather, after much has been said and little done—the only way to deter a military aggressor is by demonstrating equal resolve and superior capabilities. Diplomacy, economic sanctions, and “pre-game” rhetoric all have their place, but the actions necessary to make President Putin think again before plunging ahead with his long-range program of conquests are all military in nature, save one.
The United States should unilaterally abrogate the most recent Strategic Arms Reduction Treaty with the Russian Federation. It always has been a completely one-sided treaty, amounting to a measure of American unilateral disarmament, while Putin gave up nothing he valued or could afford to rehabilitate and keep in his arsenal. We gave up Ferraris, while Putin gave up old beaters without any wheels. Walking away from that ill-starred treaty would put Putin on notice, since his rearmament program relies on cost-savings at the strategic level.
NATO must permanently station battalion-size battle groups in each of its three Baltic state members (as tripwires), as well as a division equivalent and air wing in Poland. Temporary deployments, however regular, are no substitutes for an established presence.
The United States, in coordination with NATO and host governments, must revive and expand the missile defense program President Obama cancelled for Eastern Europe (which he did in order to get his longed-for START agreement with Moscow).
Even if NATO will not do so, the United States and other interested parties must arm, train and support the Ukrainian armed forces, which a previous president in Kiev, a puppet of Moscow, emasculated. Supplying rations is no substitute for supplying rifles, and trainers are a non-hostile-intent means of putting boots on the ground. Today, Ukraine is to Europe what Serbia was in 1914: A powder keg of disproportionate explosive potential.
The fifth and only non-military measure that would have an effect would be far-tougher and longer-lasting economic sanctions—sanctions so fierce they left the Russian Federation economically isolated and functionally crippled. Paradoxically, this is the least likely of the five listed measures to be put into effect, since Germany and other European states put profit above regional security.