"I say to the people of Estonia and the people of the Baltics, today we are bound by our treaty alliance. … Article 5 is crystal clear: An attack on one is an attack on all. So if … you ever ask again, 'who'll come to help,' you'll know the answer – the NATO alliance, including the armed forces of the United States of America."

That was Barack Obama in Tallinn, Estonia, last week, reissuing a U.S. war guarantee to the tiniest of the Baltic republics – which his Cold War predecessors would have regarded as certifiable madness.

From 1945 to 1989, no president would have dreamed of issuing a blank check for war in Eastern Europe. Our red line was in the heart of Germany. It said to Moscow: Cross the Elbe, and we fight.

That red line was made credible by hundreds of thousands of U.S. troops permanently stationed in West Germany.