When should politicians start listening to approval polls?

As I've read the news over the past couple of weeks and seen President Bush's approval ratings sag to record lows in the most recent opinion polls, I'm constantly reminded of how the President has repeatedly said that he doesn't listen to opinion polls. His stance on opinion polls, given his current approval ratings, has made me curious: at what point does a politician have to concede the proverbial high ground and change their policies (or at least day-to-day behavior) to improve the public's opinion of them? The President is an obvious target here given his past statements on opinion polls, but I think this holds true about any politician.

The most recent CNN/Gallup poll places President Bush's approval at 36 percent. In fact, according to their poll results, the President's approval rating has not been above 50% since May 5th, 2005. To be fair, this is the result of only one poll, but if you look here or here, you'll see that a fair number of other polling agencies place his approval rating below 40 percent. But despite current opinion, in November 2004 there was a popular majority of people that thought his policies were the right course for our country and voted him back into office.

Now it's clear (based on multiple opinion polls) that a solid majority no longer feel that way. Does this obligate the President to concede that the American public no longer believes his policies are the right course, and change them accordingly? The President's job is to serve the American people, so when the American public is telling him that he's going in the wrong direction, is it his responsibility to do as they say, or is it best for him to simply ignore the polls and do as he sees fit?

My view is that the President (just like any elected official) is there to serve his/her constituents. As a result, those officials should be obligated to do as their constituents desire when possible. Obviously this is not the course that President Bush will follow, but he damn well should IMHO.

Opinions welcome.