Russian President Vladimir Putin speaks with Greek Prime Minister Alexis Tsipras. | EPA Opinion 5 reasons NATO fears a Grexit With the Greeks gone from Europe, Putin would receive a major boost.

The risks of Greece exiting the eurozone are not confined to economics. The crisis poses five very real challenges to NATO that many defense officials are overlooking — at NATO’s peril.

NATO’s thin wallet will get even thinner

The crisis in Ukraine has eroded the sanctity of European security and exposed calcified remnants of Cold War divides, propelling Europe into the worst political crisis in decades. It has also proven that NATO members’ ministries of finance, not ministries of defense, dictate the Alliance’s defense posture.

Even in the face of Putin’s territorial grabs in Ukraine, still only four of NATO’s 28 members meet its required 2 percent of GDP defense spending requirement (the United States, Britain, Estonia, and, at least for now, Greece). Europe’s defense forces have atrophied since the end of the Cold War, hollowing out NATO’s deterrence posture and exacerbating the Alliance’s military stress fractures — from aging hardware to shrinking armies to grounded air fleets.

Greece dragging the Euro “to the brink” does not augur well for NATO militaries, and any market impacts of a Grexit would shift NATO members’ focus further away from defense spending.

The eurozone’s loss is Putin’s gain

Vladimir Putin is eager to chip away at Europe’s unified front in the midst of harmful sanctions against Russia. A disenchanted Greece provides Putin the perfect opportunity to seep into the expanding political cracks and fissures instigated by the Grexit debate.

Russia has already begun to seize this window of opportunity and has spearheaded new energy projects with Greece to lay political groundwork for further bilateral cooperation. As recent cases in Hungary and the Czech Republic underscore, such bilateral cooperation comes at the expense of transatlantic solidarity.

Putin himself stated that, should Greece ask, Russia may be willing to offer critically needed assistance to the economically deteriorating state. A deeper relationship between Russia and Greece would severely undermine the transatlantic community’s efforts to present a united front against Putin. If Russia makes a move to get more deeply involved in the crisis, there are few scenarios where Greece could toe the fine line between East and West successfully.

A new filibuster in EU and NATO decisions

A politically frustrated Greece could upend Alliance leaders’ decision-making capabilities. NATO relies on unanimous approval from all 28 members for all major decisions. Greece, especially one shored up with economic reprieve from Russia, could prove to be a major headache for future Alliance maneuvers to counter revanchist Russian aggression in Eastern Europe.

NATO’s unanimity clause applies not only to deploying military forces, but also to essential day-to-day functions of the Alliance such as arms sales, and major political decisions such as invoking Article 4 or 5 of the Washington Treaty to consult and defend fellow Allies. On the EU front, Greece could decide to derail EU-wide efforts to sanction Russia as the conflict in Ukraine rages on unabated.

Greece has historically stymied NATO decisions — such as through blocking effective NATO-EU cooperation because of the Turkey-Cyprus dispute. This does not mean Greece would leave the NATO or EU, or that Greece would become a “fifth pillar” of Russian influence in Europe — according to NATO’s Secretary General Jens Stoltenberg, Greeks have “really always affirmed their loyalty to NATO.” But the political fallout from a Grexit would have an indelible impact on NATO’s decision-making processes.

A crack in the dam of EU’s migrant crisis

Greece is at the epicenter of Europe’s burgeoning migrant crisis. Nearly 137,000 migrants have crossed the Mediterranean, many escaping from the conflict in Syria, to southern Europe in the first half of 2015 alone. Greece, already strained under immense economic pressure, is struggling to shoulder the burden of this refugee influx which is pushing Greece’s reception system to a “breaking point,” according to Amnesty International. Economic turmoil spurred by a Grexit will undercut badly needed funding for Greece’s ability to track refugees and retain border security. This poses a very real danger to NATO members’ security, especially as reports begin to filter in of Islamic State fighters slipping into Europe in the wave of refugees.

A bruise in the vision of Europe

Europe in the 21st century transcends geography — Europe also represents democratic ideals and values that serve as a beacon to the rest of the world. The “project” of political integration in Europe undertaken since the end of World War II through institutions like NATO and the EU has become the template for liberal-institutionalist success in the modern era; using institutions to bring together historic rivals and overcome conflicts that date back centuries and span two world wars.

Grexit poses one of the most significant challenges faced by this European “project” in the post-Cold War order. It has dealt lasting damage to every symbol the EU espouses, which harms NATO’s image by extension. While this consequence is more abstract, the crisis in Greece and potential of a Grexit have severely eroded the transatlantic community’s confidence in itself. This perhaps represents the most harmful, if diffuse, consequence of the crisis that NATO must grapple with in the decades to come.

Robbie Gramer is associate director of the Atlantic Council’s Transatlantic Security Initiative. Rachel Rizzo is a program assistant at the Atlantic Council’s Strategy Initiative.