All of us are familiar with the history of FDR and the bedrock elements of his New Deal coalition. Recently arrived immigrants, blacks and urban blue-collar whites gave Roosevelt their votes and their steadfast devotion on the electoral path to four consecutive wins.

But the foundation of this powerful coalition was organized labor — a gritty generation of working-class Democrats who would remain faithful to the Democratic Party’s brand until a steady move left in the 1960s began to strain what had been a spectacularly successful relationship.