When author David Carlin was a young man, it was scandalous for a good Catholic to be anything but a good Democrat. In the pews, pubs, and union halls of America’s cities, millions of poor European immigrants and their children pledged allegiance to the Church of Rome and the party of FDR. All that changed in the 1960s, with the rise of a new kind of Democrat: wealthy, secular, ideological. Even as Carlin served the party he loved — twelve years as a Rhode Island state senator and once a candidate for Congress — he could only watch in dismay...