That remark was always meant to be disparaging because it implied that they would move in the direction that would get them reelected rather than the right direction.
Well, thanks to Lord Monckton, we have a new metaphor for the tendency of our politicians.
Lord Christopher Monckton speaks on October 14th, 2009 at a climate skeptic event sponsored by the Minnesota Free Market Institute.
In the clip above, at about 1:28:40, after he quotes Governor Arnold Schwarzenegger pumping Global Warming, he says
"that's the traffic light tendency: they call themselves Green because they're too yellow to admit that they are really Reds."
Personally, I preferred them when they were more like weathervanes. There they exhibited more humility and tended to act more like public servants and less like rulers.