The U.S. should provide tangible diplomatic and military support to Ukraine. But it would be very ill-advised for the U.S. Navy to challenge Russia for access control over the Sea of Azov.

Russia's seizure of 23 Ukrainian sailors and 3 naval vessels is without moral or reasonable political justification. It reflects only Russian President Vladimir Putin's desire to make Ukraine a vassal state. In turn, Putin should find an international response defined by escalating sanctions and the provision of greater military equipment to Ukraine. But the Navy's entering the Sea of Azov, as suggested on Monday by the Atlantic Council's Anders Aslund, is a very bad idea.

First off, it would back Putin and the Russian ultra-nationalist movement into a corner. While the greater portion of the Sea of Azov is Ukrainian-owned (as determined by international law regarding proximate sovereign territory), Putin and many Russians see it very differently. Having seized Crimea by force and built their Kerch bridge between the Russian mainland and Crimea — an attempt to formalize Russian claims of ownership over Crimea — the Russians view the Sea of Azov as a Russian heartland. That the sea is enclosed by Crimea and Russia proper takes on added psychological significance for the Russians in that it seems divinely Russian under the mythos of Russian imperial glory. Since World War II, this mythos has been heavily rooted in the purity of Russian territory. Putin has made that narrative his own.

In that sense, for the U.S. to contest Russian control over the Sea of Azov would appear to the Russians as if the U.S. were contesting control over St. Petersburg's Kronstadt island: in short, an act of war requiring a commensurate response. Don't believe me? Then check out Russian ultra-nationalist political leader Vladimir Zhirinovsky's Twitter feed. Albeit somewhat predictably, Zhirinovsky is pushing hard for Russian escalation even in face of Ukrainian conciliation. Zhirinovsky might be a ranting, often-drunk ideologue, but he does represent a sizable constituency of populist sentiment. Even if Putin were to resist a call to arms in the event of a Navy incursion, he would be trapped by the populist feelings of the ultra-nationalists that he has so carefully cultivated over the past decade.

Put simply, if the U.S. goes into the Sea of Azov, we had better be prepared for a full-scale war with Russia. Do we want that?

The far better way to deal with Russia in this sphere is to sanction Putin and make clear that there will be no sanctions relief until Crimea is returned to Kiev's rule. Yet there's another challenge here beyond Russian political conceptions: namely, the fact that any American effort to effectively contest control over the Sea of Azov would be fraught with huge military risk.

For a start, there's the fact that the Russian southern military command literally sits right on the Sea of Azov's northeastern tip. That means a lot of Russian missile and artillery assets could rain fire down on any outnumbered U.S. warships that manage to get into the sea. Then there's the fact that Russia's Black Sea fleet is headquartered at Sevastopol, Crimea. Alongside guided missile frigates, that fleet also possesses at least five attack submarines (admittedly, it's far from clear how many are actually operational). Finally, you can bet the Russians would saturate the Sea of Azov with fighter-bomber aircraft with which to strike U.S. warships. It gets worse. Because even if we were willing to accept the thousands of casualties and wrecked U.S. warships this operation would entail, how would we actually intend to control the Crimean strait?

Would we do what would ultimately be necessary and relive the 19th century Crimean War by conducting Marine amphibious landings against Sevastapol? I think not.

The simple point here is that it is manifestly not in the American interest to conduct military operations for control of the Sea of Azov. Yes, the Ukrainians have every right to fight for every inch of their territory and would deserve moral and materiel support in doing so. But when it comes to U.S. strategic interests, we are not talking here about Russia's seizure of a NATO state's territory. In that case, such as with the Baltics, we would have to go to war. In this case, we should recognize our limitations in interest and capability and in that context apply economic-diplomatic pressure toward Putin's altered behavior.