Back in the summer of 2006, Ukraine's pro-Western government planned to host NATO exercises in Crimea as part of the alliance's Partnership for Peace program.

But when the NATO troops arrived, they were greeted with noisy, and often violent, demonstrations organized by pro-Moscow groups on the peninsula. When U.S. Marine Corps reservists tried to reach their training facility, demonstrators surrounded their bus, rocked it, and attempted to break its windows.

After days of similar harassment, the exercises were canceled.

The anti-NATO rebellion in Crimea nine years ago was just one example of how the Kremlin used pro-Moscow groups to advance its interests in Ukraine.

By using its proxies in Russophone regions to stir up trouble and infiltrate public institutions, Russia was able to create the impression that Ukraine was divided and dysfunctional -- and prevent Kyiv from making any decisive moves toward integrating with the West.

The Kremlin lost a measure of this capacity last year when it annexed Crimea, by far Ukraine's most pro-Moscow region. It would lose still more if it annexes the separatist-held regions of the Donbas -- or even freezes the conflict there. And had Moscow's ill-fated Novorossia pipe dream ever gotten off the ground, it would have lost all of it.

Every bit of territory Vladimir Putin takes away from Ukraine costs Moscow more and more of the fifth column it has spent decades developing inside the country.

This is all worth bearing in mind as Russia again masses troops on the border amid widespread speculation that a new offensive in eastern Ukraine is coming this summer.

Whether or not an offensive is, indeed, coming depends largely on what Putin wants. And what Putin wants is not exactly clear.

The Guns Of Summer

According to an eyewitness report by Reuters last week, Russia " is massing troops and hundreds of pieces of weaponry including mobile rocket launchers, tanks, and artillery at a makeshift base near the border with Ukraine."

The widely circulated story also noted that troops at the Kuzminsky firing range, located approximately 50 kilometers from the border, had removed their insignia. Vehicles there had also removed their number plates and other identifying markers.

The Reuters report added to fresh fears that the warmer weather will be accompanied by a summer offensive by Russia and its proxies to seize more territory in eastern Ukraine.

General Philip Breedlove, the NATO commander, said the separatists were using the relative quiet of the current cease-fire to regroup and rearm. Ukrainian President Petro Poroshenko told his National Security and Defense Council on May 6 that Russia had amassed 50,000 troops on the border and the separatists had 40,000 fighters inside Ukraine.

In a recent article in The Daily Beast, Michael Weiss and James Miller examined recent separatist attacks and the flow of heavy and sophisticated weaponry into rebel-held territory, concluding that "a summer offensive is inevitable."

This could well be the case. Or Russia's menacing stance could be a classic example of gunboat diplomacy.

The Stalemate In Putin's Head

Despite multiple documented cease-fire violations and fresh separatist attacks, the conflict in eastern Ukraine is deadlocked.

It's deadlocked militarily. It's deadlocked diplomatically. It's deadlocked politically.

And it even appears deadlocked inside Putin's head.

And this is because from the start of the crisis, Putin has appeared to be pursuing contradictory -- and, indeed, mutually exclusive -- objectives in Ukraine.

At times, he's seemed bent on seizing large chunks of Ukraine's Russophone east, from Kharkiv in the north to Mariupol and Odesa in the south. This would not only give Russia some key strategic ports, it would also provide a coveted land bridge to Crimea.

But achieving this objective has always been a tall order. It would be difficult -- if not impossible -- to accomplish with just hybrid-war tactics. It would probably require a full-on invasion.

"The cost of restarting the war would be high," The Economist wrote in a recent editorial. "Russia would probably be hit with a fresh round of sanctions, which could bring down its banks. It would also have to send large numbers of regular troops to Ukraine, which most Russians do not support."

Not only would a full-on invasion be costly in terms of blood and treasure, there would also be no guarantee of success. It would be a militarily difficult operation and Russophone populations in Kharkiv, Odesa, and Mariupol have proven much more loyal to Kyiv than the Kremlin expected.

And even in the event of success, achieving this objective would mean giving up on Moscow's other goal: keeping its fifth column inside Ukraine in order to paralyze the country and prevent it from moving West.

Put simply, if Putin wants one of his goals in Ukraine, he has to give up the other.

And which one he wants will set the tone for whether this conflict winds down, or whether it escalates.

Known Unknowns

So which of these objectives is Putin really after?

First, the obligatory caveat. When trying to get inside this man's head, a measure of epistemological modesty is probably a good idea. Because, in reality, we simply don't know.

We don't know what Putin is thinking. We don't know whom he is listening to. And we don't know what he is planning. We can only surmise based on his words and actions -- and those of his surrogates.

That said, my sense at this point is that the Kremlin leader is engaging in some high-stakes gunboat diplomacy.

The suspension of the Novorossia project, the assassination of rebel leader Aleksei Mozgovoi, and the Kremlin's recent rhetoric seems to suggest that a fresh offensive isn't Plan A.

Putin "wants the separatist Donbas to remain inside Ukraine, but as an open sore which Russia can prod when needed to control the country," The Economist wrote.

"Only once he has this 'political settlement' will he discuss closing the border with Ukraine. The West wants Russia to secure the border and withdraw its forces from Ukraine, so that local elections in Donbas can pave the way for its reintegration. That would defy the purpose of Mr. Putin’s exercise."

Russia's menacing posture looks like an effort to remind Kyiv and the West that if he doesn't get the Bosnia-style "federalization" he wants for Ukraine, then he might be prepared to go for broke and re-escalate the conflict.

Which doesn't mean it is harmless. The thing about blackmail is that for it to work, you need to be ready to follow through on the threat. An invasion may not be Plan A -- but it could very well be Plan B.

-- Brian Whitmore