Donald Trump’s appeasement of Vladimir Putin makes Neville Chamberlain look like a principled, courageous realist. At least Chamberlain was trying to prevent a major European war, whereas Trump is acting in the middle of one. Trump’s “Munich” (synonymous in English with the 1938 deal in which Britain and France sold out Czechoslovakia to Nazi Germany) comes on the eve of the big security conference in today’s Bavarian capital, where his emissaries will meet western allies. That Munich security conference must be the beginning of a decisive European response, learning from our own tragic history in order to avoid repeating it....