In Andrew Jackson: His Life and Times, H. W. Brands has this to say about interests and convictions:
In politics perhaps more than in most other arenas of human endeavor, interests and convictions tend to coincide. Whether convictions produce interests, or interests convictions, differs from person to person. But whatever their genesis, convictions and interests almost invariably end up pointing in the same direction. Those who can’t master the coincidence don’t succeed in politics, and they leave the game to those who can.