It was during the Depression, with the Republican regime in disarray, that Franklin D. Roosevelt came into office with a mandate to change the role of government. His was one of the presidencies--like Jefferson's, Jackson's, and Lincoln's before his, and Reagan's after--that transformed the political system. But what of the successors of such transformative figures, those members and supporters of the new regime who are expected to carry forward the policies and politics of those they replace? It is these "heir apparent" presidents, impossibly tasked with backward-looking progress, that...

It was during the Depression, with the Republican regime in disarray, that Franklin D. Roosevelt came into office with a mandate to change the role of government. His was one of the presidencies—like Jefferson’s, Jackson’s, and Lincoln’s before his, and Reagan’s after—that transformed the political system. But what of the successors of such transformative figures, those members and supporters of the new regime who are expected to carry forward the policies and politics of those they replace? It is these “heir apparent” presidents, impossibly tasked with backward-looking...