By finally inviting Montenegro to join NATO, the treaty organization has taken a significant step toward ending Russian chicanery in this small but significant Balkan country. But it will have to act fast to secure its gains. If NATO fails to close the deal, Moscow will have an opening to further destabilize the region and undermine Western interests in Bosnia–Herzegovina, Kosovo, Macedonia, and Serbia.

In principle, there is little reason to fear. Completing the process of membership requires that Montenegro iron out a few technical details regarding its accession and that the legislative branches of NATO members, including the U.S. Senate, approve the formal protocols. But all this takes time, and Montenegro faces elections in October. This creates a perfect opportunity for Russian subversion.

The potential for Russian interference was evident in October, when Montenegrin protesters and police clashed during demonstrations against the country’s President, Milo Djukaonovic. Although officials in Moscow denied Djukanovic’s allegations that they orchestrated the protests—and clearly many protesters were demonstrating over corruption and the state of the economy—speculation about Moscow’s role mounted when the archbishop of the staunchly pro-Russia Serbian Orthodox Church publicly lamented Montenegro’s separation from “Mother Russia.” Meanwhile, in neighboring Bosnia, Russia has become openly partisan in favor of the separatist Serb leaders. The Russian ambassador there recently injected himself in a tense controversy over a highly provocative referendum that could put the country’s stability in jeopardy. The idea that Moscow would show restraint next door in Montenegro, with a chance to thwart the country’s NATO bid in the balance, is farfetched.

Riot police protect themselves with shields during clashes with protesters in front of the parliament building in Podgorica, Montenegro, October 2015. Stevo Vasiljevic / Reuters

Moreover, Russia has the tools at its disposal to influence next October’s elections. In addition to the Serbian Orthodox Church and avowedly pro-Serb parties, there is residual anti-Americanism in Montenegro among leftists and green party activists. Elections in Montenegro can be competitive, with control of parliament sometimes decided by five seats or less. Dispensed liberally, Russian propaganda and money could animate the opposition, influence officials, and succeed in propelling anti-NATO, pro-Russia parties into power.

Montenegro’s accession to NATO is particularly irksome to the Russians, since it would become the first Orthodox-majority country of the former Yugoslavia to join the alliance. Montenegro also has historic ties with Bosnia and Serbia; so, should its bid succeed, NATO membership for those two countries would become a plausible, if not an immediate prospect. Serbia’s nationalist leaders, surprisingly, have already voiced their backing for Montenegro’s NATO bid, a move that must have worried Moscow, which owns Serbia’s national oil company and envisions the Balkans as part of its energy domain.

But Moscow’s outright opposition to NATO expansion is a recent posture. It was only after a NATO Summit at Cardiff in 2014 that Russian Foreign Minister Sergei Lavrov delivered the stinging pronouncement that Russia would see NATO expansion in the Balkans as a “provocation.” Prior to that, Russian President Vladimir Putin had personally informed Balkan leaders, including the President of Macedonia, another Orthodox majority country that he didn’t care if the country joined NATO. Montenegro itself, even after its bitter split from Serbia in 2006, enjoyed good relations with Moscow and attracted substantial investment from Russia despite its determined course to join NATO and the European Union. All of that changed when the Ukraine crisis erupted last year, forcing Balkan countries to choose whether or not to apply EU sanctions against Russia. While Serbia refrained from doing so, Montenegro followed Brussels’ lead, incurring the wrath of Moscow, which suddenly saw the need to frustrate Western objectives in the Balkans.

Montenegro’s accession to NATO is particularly irksome to the Russians, since it would become the first Orthodox-majority country of the former Yugoslavia to join the alliance.

For the United States, the benefits of bringing Montenegro into NATO clearly outweigh the risks of increased tensions with Russia. First, it would close the possibility of a Russian naval basing in the Adriatic, something that Moscow avidly sought last year. Second, it would anchor a country that was once firmly under the grips of former Serbian President Slobodan Milosevic into Euro–Atlantic institutions. Third, it promises to spur EU enlargement in the Balkans, which has flagged in recent years. No former communist country has joined the European Union without first joining NATO, and EU accession is a central plank in Washington’s strategy to press Europe to confront its Balkan backyard.

John Kerry meets Montenegro's Foreign Minister Igor Luksic at the NATO ministerial meetings at NATO Headquarters in Brussels, December 2015. Jonathan Ernst / Reuters

Montenegro stands to benefit, too. The country has watched from the sidelines as tourism from the United States has soared in neighboring Croatia after Zagreb joined NATO in 2009. Montenegro, whose economy is based on tourism, could use the extra source of income. In addition, NATO membership would likely attract more foreign investment. And respect for democratic values among the country’s leaders may also grow as a result of joining an alliance dedicated to civilian control of the military.

In short, the United States has ample reason to ensure that NATO membership for Montenegro becomes a reality—and to do so before Russia has a chance to skew the country’s election next fall. With the situation in Bosnia teetering, and with a heightened threat of Islamist radicalization in the region thanks to ISIS, closing the NATO deal with Montenegro is a stabilizing and feasible step to take while U.S. President Barack Obama remains in office. Election year politics in the U.S. Senate—with five senators running to succeed him—mean that the Obama administration will need to make the small country of Montenegro an outsized policy priority.