Every day seems to bring an escalation of the Russian military involvement in Syria. First it was airstrikes from more than 30 warplanes that Russia has positioned in Syria. Now it’s cruise missile strikes from warships in the Caspian Sea. Soon, if hints from Moscow are to be believed, Russian “volunteers” — a.k.a. “Little Green Men” — will be showing up in Syria to engage in ground combat alongside Iranian and Assad forces.

President Obama can pretend that this is no big deal and that Russia is getting sucked into a quagmire, but this is a serious geopolitical disaster and a major humiliation for the United States. Putin, in fact, seems to be going out of his way to target American-backed rebel groups and to send his aircraft to violate the airspace of Turkey, a NATO ally, as if to demonstrate how powerless mighty American has become and how once-weak Russia can again strut on the world stage.

Throughout the Cold War, a central American objective was to keep Russia out of the Middle East, which was then and remains now a strategically and economically vital center of energy production. Jimmy Carter launched a covert program to aid the Afghan mujahideen resist a Soviet invasion — a program subsequently expanded under Ronald Reagan — because of American fears (overblown, as it turned out) that Russia viewed the occupation of Afghanistan as a stepping stone toward invading the Persian Gulf region.

Now, however, the U.S. seems to be conceding Russia’s growing military role in the Middle East with nary a whimper – or, to be exact, with nothing but whimpers. Is a more robust response possible or desirable?

We can rule out the possibility of American aircraft shooting down Russian aircraft. That’s simply too provocative. Even buzzing Russian fighters with our own aircraft or painting them with fire-control radar runs an unwelcome risk of escalation and miscalculation. Perhaps there are electronic-warfare or cyberwar measures that the U.S. could covertly implement to disable Russian aircraft. It is, however, important to keep such action below a kinetic threshold. Throughout the Cold War, the U.S. and the Soviet Union avoided direct combat between their forces because of fears that such hostilities could escalate into World War III. The danger of fighting with another nuclear-armed state remains too great to risk today.

Slightly less provocative is the proxy option, which Obama has predictably if needlessly already ruled out. Throughout the Cold War both sides fought the other through Third World allies: the Soviets backed North Korean and North Vietnamese attacks on U.S. forces, while the U.S. backed Afghan attacks on Soviet forces. If we apply this model to Syria, the U.S. and its allies (e.g., Turkey and Saudi Arabia) would supply arms and training to Syrian fighters who would be delighted to take a shot at the Russian forces which are battling to keep the oppressive and bloodthirsty Assad regime in power.

The most effective and most risky option would be to supply Stingers or other portable air-defense systems to the rebels so they could shoot down Russian aircraft as the mujahideen did in the 1980s. Of course the American experience in Afghanistan, when we indirectly backed Islamist groups like the Haqqanis that later came to fight us, shows some of the risks of this approach. This is all the more risky in Syria because of the close links between “moderate” rebels and the al-Nusra Front, the -alQaeda affiliate in Syria: We do not want Stingers to wind up in the hands of terrorists who would use them to shoot down a civilian airliner.

Nevertheless, this is an option worth exploring if safeguards could be instituted to control access to the missiles and if the ultimate source of the missiles can be disguised. Risky as the Stinger option might be if carried out by the CIA, the risk would grow greatly if the Saudis or Qataris decide to do it on their own, because they would be likely to support Islamist groups.

It’s important to keep in mind that we don’t have to counter Russia’s power grab in Syria itself. Remember that Russia is already guilty of aggression against Ukraine, which, unlike Syria, has an internationally recognized, pro-Western democratic government. It is well past time for the president to overcome his qualms about “escalating” the Ukraine conflict by providing weapons to the Ukrainians to defend themselves.

If the Ukrainians can fight back effectively against Russian aggression, Putin will have a big problem on his hands. Already the Kremlin autocrat has gone to great lengths to conceal the casualties that Russian forces have suffered in Ukraine. That’s because he knows that Russian public opinion, while stirred up into a nationalist frenzy by his foray into Ukraine, will lose enthusiasm for the intervention if it proves too costly. Supplying arms to the Ukrainians will increase the pain of Putin’s Ukrainian offensive and divert his attention away from Syria.

So would stationing substantial American combat forces in Poland and the Baltic Republics. Putin would scream bloody murder because the U.S. had previously promised not to do so. But then Putin has violated numerous international pledges, including Russia’s commitment to respect Ukraine’s borders (the 1994 Budapest Memorandum). Putting NATO combat forces on Russia’s doorstep would be a humiliation to Putin akin to the humiliation he is inflicting on the West in Syria.

How would Putin respond? It’s hard to know for sure, but his whole pattern is that of a bully who throws his weight around when he senses weakness and pulls back when he is afraid of getting into a fight he cannot win. Note, for example, how he has scaled back his aggression in Ukraine after the West imposed serious sanctions.

Unless the U.S. does more to respond to Putin’s aggression in Ukraine and Syria, which follows his previous attack on Georgia, he will keep right on going. The Baltic States, which are NATO members, could be next in his sights, and at that point the U.S. could be facing the unenviable choice of acquiescing in NATO’s dissolution or risking a major war with Russia. Better and safer to show Putin now that there are certain red lines even he cannot cross with impunity.