I agree with Putin's post about mind-changing. I think mind-changing by a politician *can* (but need not, depending on the context) appear blatantly opportunistic, and raise legitimate concerns about whether any of his positions, past or present, was actually principled and will actually be adhered to when it becomes inconvenient to do so again in the future.
But of course, it's certainly possible for a politician to change his mind for good reasons. A good start for showing that that happened would be explaining the good reasons.
Things I've changed my mind on:
1) I used to find the doctrinaire Republican case against illegal immigrants compelling. I no longer do. (My positions on this would still be moderate conservative).
2) I used to think George W. Bush's use of executive powers was reasonable and unconcerning, and I no longer do. However, while I'm also concerned about the current administration's abuses (as I see them), I recognize that its supporters have the same motivations not to see them that way that I had when Bush was President, so I can't well complain if they deny such abuses. I only hope that the next President, whoever that may be, will be held accountable by people of both parties for their use of executive power.
3) I feel pretty ambivalent about what the legal status of various drugs should be, and my opinion could be described as a slow oscilation without high confidence. I hope that it will settle and my confidence increase. Arguments on this board have been among several that have augmented this ambivalence.
4) I have come to accept the Miami Heat's right to exist, although I'm not at all happy about it.