Why has Obama moved ahead? The pollsters cite Sarah Palin's drop in popularity in the state. They write:
A precipitous drop in Sarah Palin's approval may be helping to fuel Obama's gains. Immediately after the convention 41% of Colorado voters said that her selection made them more likely to vote for John McCain, compared to 38% who said it made them less likely to do so. Since then there's been a 12-point drop in her net favorability. Now just 38% say that she makes them more likely to vote for the Republican, with 47% saying their less likely to.
The drop in Palin's popularity is not surprising given her newness on the national political scene. That newness, combined with continuing questions about her record in Alaska, was bound to cause problems for the governor.