There is a popular button/bumper sticker that reads: If the people lead, the leaders will follow. Like a lot of adages, there is much truth here. Particularly in an ostensible democracy, leaders want to appear that they are on the side of the people to keep the votes coming. If the people exhibit a significant majority opinion on an issue, political leaders will fall all over themselves trying to convince the people that they have always been on their side.
Look at what has transpired recently on the issue of gay marriage. As it appears more certain that the US Supreme Court will validate gay marriage in one respect or another, politicians who for years were against the concept or, at best, non-committal, all of a sudden are coming out of the woodwork to say they support it! What changed their minds? They don't want to be viewed as coming out on the wrong side of history! Come out on the wrong side and the chances that you will be reelected or elected diminish significantly.
The same thing happened this past year in my state. As poll after poll indicated that the initiative to legal marijuana was likely to pass, politicians who had been steadfastly against it experienced sudden epiphanies. Calling hastily scheduled news conferences, they would stand before the cameras and microphones to voice their "heartfelt" support.
While it is certainly true that each of us can change our minds about important issues, it is the timing of the change of heart by politicians that is so amusing. It goes back to the adage in the first sentence.