As mentioned earlier, the recent Marquette poll was grossly misweighted toward conservatives at the expense of moderates and liberals. If we average the the last three Wisconsin exit polls (06, 08 & 10) you can see just how far away from the actual electorate that this poll strayed:
Considering that the Marquette poll showed that Walker wins conservatives 72% to 22%, while Barrett wins moderates 50%-41% and liberals 83% to 15%, grossly misweighting the poll in favor of conservatives is, of course, going to result in the best possible Walker result.
However, if we weight the Marquette poll according to the exit poll, aka the actual electorate, we find that Barrett leads 49-45.
Do I believe Barrett is ahead by four points? No way. But, I also don't believe that Barrett is behind by six points. I think both candidates are right around 46% with the momentum trending toward Barrett.