As in physics, so in politics: for every action there is a reaction, perhaps not equal nor precisely opposite, but reliably contrary nonetheless.
–David M. Kennedy, Freedom From Fear: The American People in Depression and War, 1929-1945 (1999), p. 339
We have all been taught to regard it as more or less “natural” for young dissenters to become conservatives as they grow older; but the phenomenon I am concerned with is not quite the same, for it involves not so much the progression from one political position to another as the continued coexistence of reformism and reaction; and when it takes the form of progression in time, it is a progression very often unattended by any real change in personal temper. No doubt the precise line between useful and valid criticism of any society and a destructive alienation from its essential values is not always easy to draw. Some men, and indeed some political movements, seem to live close to that line and to swing back and forth across it more than once in their lives. The impulses behind yesterday’s reform may be put in the service of reform today, but they may also be enlisted in the service of reaction.
—Richard Hofstadter, The Age of Reform: From Bryan to F. D. R. (1955), p 21