Half a century ago, one of the big topics of debate in Washington and on the St. Louis Post-Dispatch editorial page was: Why don’t European nations contribute more to NATO?

Only back then, Republicans were the ones arguing forcefully for U.S. sacrifice on NATO’s behalf, while Democratic Senate Majority Leader Mike Mansfield was NATO’s fiercest critic. Today, Republican President Donald Trump is the one taking up Mansfield’s mantle.

Mansfield in 1971 proposed that U.S. troop levels in Europe be cut in half to force European nations to pony up a fairer share for their own defense.

Mansfield was correct back then, and Trump is correct today, on the need for Europe to do more. Our issue is with Trump’s insulting and undiplomatic delivery of that message.

Mansfield’s anti-NATO campaign came only three years after the August 1968 Soviet-led invasion of Czechoslovakia to put down the “Prague Spring” breakaway reform effort. Today the same debate rages only four years after Russia invaded Ukraine, shot a passenger airliner out of the sky, armed a separatist rebellion and annexed Crimea. Moscow’s expansionist desires haven’t diminished in 50 years, which is why NATO’s importance must never be underestimated.

Trump’s caustic demeanor only helps advance Russia’s goal of fomenting division and weakening the most important mutual-defense alliance the world has ever known.

Amazing how one leader can be so right, and yet, at the same time, so wrong.