The destruction of Malaysia Airlines flight 17 over eastern Ukraine by a surface-to-air missile will likely prove to be a watershed moment in this 21st-century European war and the regime of Russian President Vladimir Putin.

In order to understand its impact, we first need to try deducing the Kremlin’s plan before this tragedy. Obviously, only those closest to Putin know his intentions, and it is quite possible he has not come to a final decision about his Ukraine policy. Although many like to depict the Russian president as a cold, long-range calculator, indecision seems more likely: if the Kremlin were fully committed to the annexation of eastern Ukraine, it would have done so already.

Russia certainly had the means for annexation when the rebellion erupted, with troops massed along their shared border and the Ukrainian military demoralised over the humiliating loss of Crimea. Putin’s statements about the illegitimacy of Novorossiya’s (New Russia’s) incorporation into Ukraine after the Russian Civil War and a series of separatist-run referendums in eastern and southern Ukraine laid the rhetorical and political foundations for such a move. There are obvious differences between Crimea and the other contested areas — particularly in their geographic size and the percentage of ethnic Russians — but the lack of an open irredentist campaign implies that the Kremlin got cold feet. Instead, it adopted a strategy of covert support for the separatists through training, arms supplies, and limited Russian Federation involvement.

It is perhaps telling that Russia Today, the Kremlin’s English-language mouthpiece, used slightly different language when discussing the separatists in Crimea versus its current references to separatists in other parts of Ukraine. For example, it referred to the “Republic of Crimea” as if it were an incontrovertible fact, but refers now to the primary separatist regions of the Donetsk and Luhansk people’s republics as “self-proclaimed“ — implying something more ephemeral, with less legitimacy.

The Kremlin’s public call to delay independence referendums and its refusal to immediately agree to the regions’ ascension to Russia contrasts sharply with its quick annexation of Crimea. Moreover, the Russian separatists have lost significant ground over the past few weeks without a military reaction by the Russian Federation in defence of its “compatriots” abroad. It is possible that the proxy war is laying groundwork for a Russian invasion in August or September, as suggested by some, but we cannot be certain. It is just as likely that Putin is playing for time, uncertain of his ultimate goal: the creation of a greater Russia or simply a weak and fractured Ukraine? The current crisis may actually reinforce the Kremlin’s indecisiveness.

In Russia, Putin is currently riding a wave of unbelievably high popularity, with an approval rating of 83%. It is too early to tell how the MH17 incident will impact this. Those Russians able to see through the Kremlin’s misinformation may reject being accomplices to mass murder and turn on the government. However, given the effectiveness of the propaganda machine in Russia, this will be evident only in the margins. The real danger for Putin is in the monster of his own creation — rabid nationalism.

Putin’s popularity is built in large part upon nationalist and xenophobic sentiments promoted by the Kremlin. This is fueled by an assertive foreign policy in the former Soviet Union and beyond, the championing Russia’s great power status, and the image of Putin as the primary defender of the Russian people. The annexation of Crimea reinforced all three of these factors and added a new designation for Putin, revived from the tsarist era:  “the gatherer of Russian lands“.

The problem now for Putin is in eastern Ukraine. The covert campaign has kept his popularity high, since the Russian media has depicted Putin as indirectly continuing the good fight against the forces of Western/fascist evil. However, any let-up in the Kremlin’s support for the separatists, or signs that Putin is submitting to the West, will have a negative effect on his popularity. This is especially true if the separatists continue to lose ground to the central forces — a real possibility given recent Ukrainian military gains. This would be a political disaster for Putin. Nonetheless, the Kremlin’s support for the separatists may very well wane as a result of the destruction of MH17.

Most western European countries were more than willing to ignore the conflict in order to avoid upsetting relations with the Kremlin, keep their energy supplies coming, and continue doing business with and in Russia, but this mass murder of primarily European civilians makes this impracticable. An alliance between eastern Europe, which has heretofore argued futilely about the Russian threat, and the Netherlands, which lost a greater proportion of its population on July 17 than the United States lost on 9/11, may be able to shake up the European Union’s current policy inertia of symbolic responses to the Ukrainian crisis. Serious sanctions against Russia are now on the table, though their passage remains unlikely in the short term since the interests of France and Germany appear to be blocking any substantive policy changes.

Nonetheless, a sea change against Russia has occurred in the court of Western public opinion. Any possibility that the Kremlin could play a constructive role in the resolution of this conflict has been exposed for the delusion it has always been. Instead, Putin’s Russia is seen as a malevolent force. Any blatant Russian aggression in Ukraine — most likely an attempt to rescue the separatists from defeat — may serve as the proverbial straw that broke the camel’s back. This would have the unintended effect of finally galvanising Europe to resist the greatest danger to the continent’s peace and stability since the end of the Cold War: Russian aggression. In such a circumstance, even the fence-sitters will be compelled to react in a serious, punishing way.

It is difficult to believe that the Kremlin does not understand how serious this possibility is. Real, substantive sanctions run the risk of further undermining the Russian economy, which desperately needs continued foreign investment to avoid being reduced to a rentier state, relying almost entirely on the export of its natural resources. This possible future is something Putin cannot tolerate, since, in addition to nationalism, the other foundation of his popularity rests on the increased living standards for ordinary Russians. Given these conditions, the Kremlin’s already evident hesitancy in Ukraine may become more prominent.

And thus, the tragedy of MH17 has backed Putin into a corner: either he can push forward and run the risk of increased confrontation with the West, which Russia can ill-afford, or he can abandon the separatists and become known as the traitor to Novorossiya and Russia’s great power status. His choice will determine the shape of Europe for the foreseeable future.