why it is a changed political landscape

Today the CNN/USA Today Gallup Poll also shows Bush's lead gone (they had him 8 pts up). So Howard Kurtz, the erstwhile conscience of the Establishment press, fesses up to why the polls (like negative commercials) are important: because they drive the media coverage. His column also contains a tidbit of the Fox faux pas mentioned here earlier.

A Changed Political Landscape, Or an Isolated Peak in the Polls? (washingtonpost.com)

Why is the correct answer: the landscape has changed? Partly because it's so close to the election. Partly because Bush's unfavorables have been high even when he was leading, so the stage was set for Kerry's move up when he showed credibility. And because Bush's credibility has been hurt, which blunts the effects of his negative commercials and negative statements on the stump, since they were already effectively countered in the debate.

Not that it's over by a longshot. But this race is at least even until the end, barring some major miscue or Surprise.