STUTTGART, Germany -- If Sunday's referendum that rejected new austerity measures turns out to be a prelude to Greece's abandonment of the euro, the country's position inside the NATO military alliance also could be jeopardized.
Already Russia has been reaching out to the leftist Greek government.
One day after Greek voters rejected new terms for an international bailout, Russian President Vladimir Putin telephoned Greek left-wing Prime Minister Alexis Tsipras and expressed his support for the Greek people, a Kremlin statement said.
Recent displays of friendship between the two Christian Orthodox countries have been mutual. After casting his vote Sunday, Greek Defense Minister Panos Kammenos told journalists in Athens that Russia is not the enemy but a "brother country." Back in February, Kammenos was issuing warnings that his country could pursue a "plan B" if a more favorable bailout deal couldn't be reached, indicating Moscow could be a possible benefactor.
Historically, Greece has maintained closer cultural ties with Russia than most other Western nations. Now with Greece in financial shambles, some observers fear that European leaders' failure to reach a compromise on bailout terms could push the country toward Russia and eventually challenge NATO's ability to maintain solidarity in dealing with Moscow.
Plenty of questions remain about the implications of Sunday's vote.
In theory, Greece could find itself out of the eurozone but still in the EU and NATO. That raises a host of thorny concerns.
Retired Adm. James Stavridis, a former NATO Supreme Allied Commander, warns that alienating Greece will have long-term geopolitical consequences.
"Let's face it: A Greece that goes crashing out of the eurozone will be an angry, disaffected, and battered nation -- but one that will continue to hold membership in the European Union and NATO, both consensus-driven organizations," Stavridis wrote in a Foreign Policy commentary ahead of Sunday's vote.
NATO, an alliance of 28 countries, requires unanimous consent to make major decisions. For example, when members recently agreed to expand NATO's response force from 13,000 to as many as 40,000 troops, a move sparked by concerns over a more assertive Russia, the alliance required Greece's consent to do so. If the time ever comes to deploy NATO's new brigade-size spearhead force on a crisis-response mission, that also will need Greek approval.
"In both the EU and NATO, an uncooperative Greece in the future could time and time again put the organizations 'in irons,' which is to say becalmed and not moving effectively forward," Stavridis warned.
In the case of the EU, which has struggled to stay united on sanctions against Russia for its illegal annexation of Ukraine's Crimea Peninsula, Greece could break Europe's fragile unity.
As for NATO, officials declined to speculate about the future of Greece or outline what steps would be required if the time ever came to evict Greece from the alliance.
"The secretary-general has made clear that Greece is a committed ally, and the Greek government has stressed that they stand by their commitments to NATO and do not make any link between the debt crisis and Greece's NATO membership," a NATO official said Monday.
According to NATO's Washington Treaty, a member is free to renounce membership and leave the alliance one year after submitting formal notice of departure. The treaty doesn't specify how allies would evict a member it deemed at odds with NATO interests.
As Greece's crisis with the EU has dragged on, leaders have increasingly been looking toward Moscow for possible relief. While Russia's ability to provide support could be limited -- Moscow itself is in a bad fiscal state -- Putin has made a point of meeting with Tsipras, much to the West's consternation.
Still, some experts doubt Greece would ever attempt to exit NATO, despite Athens' contentious relations with EU.
"Because of the Cyprus issue and Turkey, not to speak of the turmoil in the Middle East, NATO is crucial to Greece's security," said Judy Dempsey, an expert with the Carnegie Europe think tank in Brussels. "I can't imagine what the military would do if there was any move by the ultraleft and ultraright in Tsipras' coalition to even call into question the Alliance. Not to speak about how the U.S. would do everything to keep Greece inside NATO."
For the U.S., Greece's troubles and the EU's tough stance on austerity have long been a source of concern.
Stavridis cautioned that a Greece estranged from Europe would prove destabilizing for the Continent as a whole. European politicians must take into account the geostrategic stakes of a Greek default and departure from the eurozone, he said.
"At the dark end of the spectrum, losing any nation from the EU or NATO is simply terra incognita and would shake both organizations in fundamental ways while deeply weakening the idea of the European project generally," Stavridis wrote.