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. Yet Truman did not use force to break the Berlin Blockade. Ike did not use force to save the Hungarian rebels. JFK fulminated, and observed, when the Wall went up. When Leonid Brezhnev sent Warsaw Pact armies into Czechoslovakia, LBJ did nothing.

Why did these presidents not act? None believed there was any vital U.S. interest in Eastern Europe worth a war with Russia.