Republican Senators Rand Paul and John McCain recently exchanged heated barbs on the Senate floor over Montenegro’s potential membership in NATO. Why did alliance membership for the Balkan republic lead to such an acrimonious debate between the occasional senatorial sparring partners?

At War on the Rocks today, I have a piece with Benjamin Denison, a PhD candidate at the University of Notre Dame who specializes in Balkan security, discussing the debate over Montenegro’s accession to NATO. We argue that Montenegro does not fit the standard criticisms lobbed at new NATO members, that Montenegro provides small but real benefits for the alliance, that reneging on the agreement would have damaged American credibility in the region, and that NATO critics wasted political capital better used to fight attempts to further expand the alliance into Russia’s periphery in the future.

From our piece:

The energy and political capital used by critics, such as Paul, to argue against Montenegro’s membership in NATO should instead have been saved for future potential fights over whether to offer potential NATO membership to Ukraine or Georgia. While neither former Soviet republic was offered a NATO Membership Action Plan, despite a strong push by the Bush administration at the alliance’s 2008 summit, there are those who still wish for them — and even Moldova — to one day become members. But these states are exemplars of the case against NATO expansion.

Unlike Montenegro, both Ukraine and Georgia are located directly adjacent to Russian territory. Both have been involved in conflicts with Russia in the past decade. Russia continues to intervene on behalf of separatists in both eastern Ukraine, and Abkhazia and South Ossetia in Georgia — with Moscow exerting leverage by issuing Russian passports to citizens of those territories. Even if Russia were not already so deeply involved in both Ukraine and Georgia, adding them to NATO would add new — and costly — military requirements for existing NATO members. Given the disproportionate role of the United States in NATO’s military architecture, the need to deter even potential Russian aggression along its periphery would add to the United States’ defense requirements — as the inclusion of the Baltic states in NATO already has.

Read the entire piece here.