For the last week, John McCain was an average of 2% ahead of Barack Obama in national polls. But this weekend the gap closed after a widely viewed television performance by McCain. In polling through Saturday, the median margin is now a tie: 0.0 +/- 1.1%. In five surveys conducted September 10-13, the margins were

Rasmussen Tracking – McCain +3%
Gallup Daily Tracker – McCain +2%
Newsweek – Tie
Diageo/Hotline – Obama +2%
Research 2000 – Obama +2%

What caused this slight but noticeable shift? It could be John McCain’s appearance on The View, which highlighted his opposition to Roe v. Wade and his repetition of his campaign’s lies. Or the growing awareness (survey data) of Sarah Palin’s degree of readiness for office (continuing with a funny takedown on Saturday Night Live). Or post-convention enthusiasm could simply be wearing off. Whatever the cause, opinion is moving.