One of the things that has struck me about US presidential elections (not just this one, but the previous ones as well) is the hysteria with which any evidence of a change of opinion by a candidate is greeted. A new take on any issue from an individual is called everything from a flip-flop (with its connotations of floppiness and indecision and unreliability) to words like betrayal and lack of principles. The press and the opposition scour the voting records of candidates to find inconsistencies and then treat them with scorn.
True, a politician who blows this way and that depending on a political wind is a bit of a useless reed, with no backbone and adhering to no principles because he doesn't actually have any. But let's not go overboard on this.
A politician who changes his mind is not necessarily an unprincipled idiot. Quite frankly, when it comes to a job like the President of the USA, I'd appreciate knowing that the world has in it a president of a powerful country who actually was capable of weighing up an issue and deciding that new developments warranted new directions. That seems like wisdom to me, not a lack of principles.