As a reactionary, I've long viewed politicians as being, at best, whores. So what should we set as the expectation of our public harlots?
My take is a politician taking a new position during an election cycle is reasonably acceptable, as long as he votes commensurate with that new position if elected. Election year is in fact the most reputable time for a 'flip-flop'. What is not acceptable is running, say, as a pro-gun politician and betraying those voters who thought they were buying a pro-gun temporary liason or vice versa. Nobody should have any indignation that someone who supported an issue, say, in the 1980s does not do so now.
Expecting politicians to be paladins and exemplars of particular issues is a recipe for disappointment. Instead, here's the questions:
Is he willing to be your whore on this issue?
Does he have a history of staying bought for the election cycle?
Yes, occasionally you'll get a 'true believer' on an issue, and having them around is very nice, but that's no way to assemble a working majority to defend your interests. To do that you need to learn how to employ the mercenary who will stay bought.