Russia’s drone incursion into Poland overnight, forcing NATO fighter jets to scramble and shoot down some of the drones, was an enormous escalation by President Vladimir Putin of Russia. And for those of us in the West, it was a test.

It was a test, first of all, of whether we will take this violation of NATO territory seriously, or whether we will investigate, wring our hands and debate among ourselves whether the drone incursion was real. A lot about the event is still being figured out but this incursion appears intentional. One drone might go astray, but this was more than a dozen drones entering Polish territory, even as none appear to have been reported in Slovakia, Hungary or other neighboring countries.

That’s how Putin operates: He tests and measures the reaction. If this challenge to NATO is met with nothing more than indignant tweets, he will escalate further. He is trying to bully NATO countries into backing away from Ukraine, as he has bullied so many others.

This is not unexpected. Military officials have long been concerned that Putin might intensify Russia’s war in Ukraine by striking Ukrainian supply lines in Poland, but until now he apparently has calculated that the risks are not worth it. I wonder if he believes that President Trump’s refusal to hold Moscow accountable so far makes this a good time to see if he can get away with attacks on NATO territory.

“Putin is testing our resolve to protect Poland and the Baltic nations,” noted Senator Dick Durbin of Illinois. “These incursions cannot be ignored.”

Indeed, the West should respond in a measured way that raises the costs to Russia of this incursion and deters it from further attacks. That means inflicting pain, not speeches, on Moscow — even as we resist slipping into a broader war that entails risks of nuclear escalation.