President Bush can lose Ohio and still make it to 270 with Wisconnsin and another small battlegound state. If, however, Kerry loses OH, he is done.
See the RealClearPolitics analysis: http://www.realclearpolitics.com/Commentary/blog_10_8_04_1011.html
Plus, President Bush seems to be up in Winsonnsin, however the polls here are a bit old:
http://www.realclearpolitics.com/Presidential_04/wi_polls.html
The analysis stands even though I have trouble spelling Winconsin :-)