Sam Rosenfeld says FDR eventually did what many wish Obama would do — challenge the troublemakers in the party.

Franklin D. Roosevelt began his “fireside chat” on June 24, 1938, as he had begun others, recounting New Deal battles won and lost during the most recent congressional session. But he ended the broadcast with a surprise. “And now,” the president intoned, “I want to say a few words about the coming political primaries.” In this midterm primary season, he said, “there will be many clashes between two schools of thought, generally classified as liberal and conservative.” Roosevelt insisted that, as “head of the Democratic Party,” charged with carrying out “the definitely liberal declaration of principles set forth in the 1936 Democratic platform,” he had an obligation to speak out about primary contests involving such a clash. Thus did Roosevelt announce a political gambit not attempted by any president since: active and personal intervention in key primary contests, not only to protect liberals but to replace conservatives. The press branded the effort a “purge,” and the name stuck.

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