http://www.cnn.com/ELECTION/2004//pages/results/states/WI/P/00/epolls.0.htmlhttp://www.cnn.com/ELECTION/2004/pages/results/states/WI/S/01/epolls.0.html45-60+, independent or republican, ideologically more moderate.
So basically a moderate or independent leaning republican voter who liked Feingold despite voting for Bush. and maybe even wanted a democrat as a senator for wisconsin or at least as a check on Bush by not voting for a republican for senate. Also his swing was strongest in rural areas/less populated counties.