A senior Russian Foreign Ministry official says that Moscow has a responsibility to protect ethnic Russian citizens of other countries, "regardless of where they live," and that "we will do everything possible to defend the rights and interests" of ethnic Russian minorities in the neighboring Baltic states of Estonia, Latvia, and Lithuania.

The comments came from Anatoly Makarov, the director of the Foreign Ministry's Department for Interaction with Compatriots Abroad. He was speaking to the Russian outlet RuBaltic, as translated by Paul Goble. "We are carrying out a line so that Russian compatriots regardless of where they live are guaranteed all rights and freedoms ... and have the opportunity to preserve the culture and traditions of their historical Motherland," Makarov said, explicitly extending this to the million-plus ethnic Russians who are citizens of Baltic countries.

Here's why that's a bad sign: Russia premised its two invasions of Ukraine (first to annex Crimea in March, then to invade eastern Ukraine in August) on protecting ethnic Russian and Russian-speaking minorities in the country. And Russian President Vladimir Putin's government has embraced the imperial-era idea that Moscow is the real authority responsible for ethnic Russian minorities in other countries. The fear has always been that Putin might extend this thinking to Russian minorities in the Baltic states, as possible prelude to a Ukraine-style invasion there.

The threat of possible Russian meddling or outright invasion in the Baltic states isn't just that another invasion is bad. It's that it could — and I am not exaggerating here — spark World War Three. Unlike Ukraine, the Baltic states are all members of NATO, a mutual self-defense treaty that includes all of Western Europe, Canada, and the United States. A Russian invasion would trigger war with all of those countries, which also happen to include the world's four most heavily armed nuclear powers. That's an extreme outcome, but not entirely out of the range of possibility.

Putin may well be merely testing his limits in the Baltic states, which is probably why President Obama himself flew to Estonia and gave a speech warning Russia that the American military would defend it and other Baltics from any Russian aggression. Less than 48 hours later, though, Russian agents crossed the border into Estonia and kidnapped an Estonian state security officer who works on counterintelligence. While far short of an act of war, it certainly seemed like a provocation intended to signal Moscow's willingness and desire to bully its Baltic neighbors, NATO mutual defense treaties be damned.