The shadow cast over the West by Britain’s vote to exit the European Union will not be dispelled anytime soon. But a summit of the NATO alliance in Warsaw over the weekend provided a ray of light.

By ratifying decisions to deploy forces in Eastern Europe to deter Russian aggression and extend the military mission in Afghanistan, NATO and its leaders confirmed that their defense cooperation remains functional and able to respond to new challenges. It was a demonstration that surely disappointed Russian President Vladimir Putin — and ought to be instructional for presumptive Republican presidential nominee Donald Trump.

Not without reason, President Obama called the Warsaw decisions “the most significant reinforcement of collective defense any time since the Cold War.” NATO will send four battalions of 800 to 1,200 troops to four countries: Poland, Latvia, Lithuania and Estonia….

While a battalion wouldn’t stop a Russian invasion, it will provide a tripwire that could deter impulsive and opportunistic adventures by Mr. Putin — as the invasions of Crimea and eastern Ukraine appeared to be.

Mr. Putin, who cheered the Brexit vote and hoped for a split within the West, will have to witness the deployment of more NATO troops to his borders as well as the renewal of Western economic sanctions linked to Ukraine; prodded by the Obama administration, the European Union renewed its version of the measures last month. Moscow could respond with its own military exercises and patrols. But it has already been provocatively prodding its NATO neighbors for years. Now it will face a more determined response.

Image: UK Prime Minister David Cameron and President Barack Obama at the NATO summit in Warsaw, July 8, 2016 (photo: NATO)