Should the North Atlantic Treaty Organization start arming Ukraine? That's an inevitable question following the entry of regular Russian troops, tanks and artillery into the fight there.

The answer was self-evident to a number of Ukrainians (and liberal Russians) at a conference this week in Salzburg, Austria: Of course NATO should send arms. Not only is it fair -- the U.S. and European powers signed a security guarantee for Ukraine in 1994 in exchange for the government in Kiev giving up its large nuclear arsenal -- it would also be proportionate to the threat.

Ukraine Crisis

Andrei Illarionov, a former chief economic adviser to President Vladimir Putin and now among his fiercest critics, described how the parliament in Moscow has passed legislation to enshrine Putin's vision of a new "Russian World" stretching from the middle of Ukraine to northern Kazakhstan. To help realize this post-imperial dream, Moscow asserts the right to intervene militarily on behalf of Russian speakers in its near abroad. "The only result can be war," he said.

Each Russian military success would breed further appetite while attracting admirers of the Putin style. Already, Hungary's leader, Viktor Orban, has begun to talk about the appeal of Putin's authoritarian approach compared with the perceived weakness and decline of liberal democracies.

I'm not so sure. The U.S. and Europe have made it clear that they will not go to war with Russia -- a nuclear superpower -- to defend Ukraine's borders. That may not be fair, but it is rational. And no matter how many weapons the U.S. and European allies supply to Ukraine, Russia will deploy more of them, wielded by better trained troops.

The logical progression of a NATO armament program for Ukraine is broader conflict. Putin would proceed, knowing that, in the end, Ukraine's allies would not have its back. The calculation could change if Putin decides to push his military deeper into Ukraine -- realizing fears of a wider conflict while heightening the security concerns of nearby Poland. For now, however, a formal arms program seems unwise.

Absent a willingness to go to war on the part of NATO, the most potent weapons against Putin's adventurism are economic, and long-term. Genuine, sectorwide economic sanctions that tip Russia's economy into a deep recession may make him rethink how far he wants to go in Ukraine, or whether to repeat such belligerence elsewhere. A clear signal that Russia's wider security would suffer may also have an impact. For example, before this year, there was minimal popular support for the idea of joining NATO in Ukraine and zero interest in pushing that idea within the alliance. A guarantee not to join the alliance could be part of any settlement, but membership can also return to the agenda if Putin continues. Similarly, nonmembers Finland and Sweden decided this month to sign a pact with NATO that will make it easier for alliance forces to deploy on their territory. None of these developments are welcome for the Kremlin.

The NATO summit next week looks set to facilitate some important decisions. For example, what level of forces should rotate "persistently" through planned logistics bases in Poland and the Baltic States? (Answer: a lot.) NATO must also decide how much money to put into four proposed trust funds dedicated to helping Ukraine cover the costs of military training, cyber-defense, logistics and other needs. (Same answer: a lot.) The U.S. and Europe should give Putin every possible signal that they are prepared to ensure Ukraine's survival as a state, short of war.

If Illarionov and other alarmists who compare Putin's Russia to Germany in the late 1930s prove right (and me wrong), not even war can be ruled out. For now, though, it's up to Putin to decide how far he wants to go in triggering a new Cold War, and at what cost.