Ideological Betrayal, Left and Right
I noticed a recent article in Mother Jones, The Seduction of Paul Wellstone, about a politician who took office as "the Senator from the left" but apparently failed to live up to his supporters' hopes. The implication of the article is that such a failure is a likely, but not inevitable, result of the collision between ideological commitment and the politics and culture of Congress.
The article did not discuss the issue from the other side, Republican politicians who started outside the usual range of their party. No doubt one could find examples of the same pattern. On the other hand, Ron Paul provides a striking example in the other direction, a libertarian Republican who did, mutatis mutandis, what Wellstone's initial supporters hoped he would do—remained true to his principles, and made a serious effort to raise public support for them.
It remains to be seen whether other libertarians, most obviously Rand Paul, will follow his path or Wellstone's.