This.
And if the alliance doesn't come apart from external pressures in the Baltics, just wait until NATO's hyper-expansionism into the Balkans fully plays out and it ruptures internally right down the Western side of the peninsula. Ultimately, the EU and NATO are no longer tied together by common objectives for the region, and that is untenable moving forward when mutual defense obligations contradict EU expansion objectives.
And there are endless possibilities for mutual defense contradictions if every country down there is guaranteed protection from attack through Article 5. Just as an example, take the good and righteous government in Albania. Sure, ever-wise John McCain and peace-loving Lindsey Graham never tire of speaking of the wonderful and freedom-loving people of Albania, but the population of every NATO member country in the EU is fully aware that Albania is a fully corrupt narco-state enabled by Washington, run by gangsters in Tirana, and increasingly full of ISIS sympathizers out in the poorer rural areas. And if Albania is Michael Corleone, it's client-quasi-state next door, Kosovo, is Sonny: Far less intelligent and far more out of control. And NATO is in bed with those maniacs and the EU populace is well aware of it.
So, since NATO membership is essentially viewed by those countries as a required stepping stone to the EU and nothing more, the closure of the path to the EU's free movement and free money will make NATO far less important to the citizenry. The EU is going to let Serbia in at some point given how many accession chapters the Serbs have already completed. There will be pressure for Bosnia to eventually accompany, but Bosnia is a volatile dump without much going for it and is still a powder keg. If Serbian admission happens, the repeated delays by Brussels, year after year, to even consider many of the newer NATO additions like Albania and Macedonia for admission is going to end up causing some volatile electorate down there to get more irrational than they already are. Along will come some irredentist asshole like the current ones in Edi "Greater Albania' Rama or Bush/Clinton's Favorite Drug Lord/Human Organ Trafficker, Hashim Thaci in Pristina, whose key to unlocking more and more power is to get more and more ethno-nationalist and aggressive towards some neighbor that they have hated for centuries. Because the Balkans are gonna Balkan and NATO isn't nearly big enough of a carrot anymore to change that instinct.
Eventually, NATO membership becomes much less valuable when no one really takes it seriously, which is what is happening when the locals are "in the know" about how exaggerated the Russian threat truly is. Which they very well do. Those people down there don't see NATO as a protector from The Bear. They see NATO much more for what it did for Bosnia and Kosovo and they want a bodyguard to protect, both from their aggressors, as well as from retaliation when it misbehaves.
Despite our preference for nice, clean Good vs. Evil war propaganda, in the Western Balkans, it's just a bunch of Darth Vaders with zero loyalty to "Western Values". Stupid to commit to protecting all of them from one another, but in true fashion, that's what we are doing. Won't last.