Today, the most important military alliance in the world turns 72. After four decades of defending Western Europe against the Soviet threat, in the 1990s NATO halted and rolled back some of Europe’s worst atrocities since the Holocaust. After 9/11 brought the alliance into missions far from its normal sphere of operations, Vladimir Putin’s invasion of Ukraine brought home just how important its original mission still is. Today, while a man who foolishly treated NATO with contempt is out of the White House, the alliance must still make clear why it is needed.