National security will always be the number 1 priority with the kind of neighbour Latvia has.
They are still finding pockets of exiled Latvians deep inside the Russian interior, and asking them if they want to come home.
Take a look at what happened to Cyprus. They (the EU) would never do that to Italy, no matter how crisis-striken would ever be. Meaning: Say tomorrow Russia invades Latvia, the EU will do a couple statements and that's about it.
Latvia can always invoke Article 5 of the NATO treaty, anyway.
Apart from that the majority of states in the NATO are also EU member states, meaning that the EU has effectively control over the NATO. Also something that might be worth considering in such a scenario.
I liked the jackboots in the previous version, I hope you'll find a way of putting that back in!