The principle that democratic nations have the right to govern themselves free from fear of invasion is paramount.

Overtly deploying military forces into southeastern Ukraine on Monday, Vladimir Putin has shredded that principle. The Russian president insists that his action is designed only to defend Russia and ethnic Russians in Ukraine. But this is not true. Ukraine poses no credible threat to the Russian Federation. Ethnic Russians in southeastern Ukraine are not targets of the Ukrainian military. Putin’s aggression is a clear-cut assault on international order and European security. And Putin now threatens a far wider offensive against Ukraine.