I think Kohl has an election year coming up (I am from Wisconsin and ashamed I don't know this) and Feingold had a close battle with a very conservative candidate back in 04. Also Bush barely lost this state.
It is very obvious Feingold and Kohl are trying to come across as moderates when they are among the biggest libs in the senate. Both of them voted against the partial birth abortion ban which resulted in a recall effort.
I think the Democrat vote was completely choreographed, including Leahy's Yes vote. They had to show the leftists they had some spine to stand up to President Bush, but by allowing a few to vote Yes they think they have sent a message to the White House not to send up a "more conservative" nominee next time, and to the American people that they can be "reasonable" if given "reasonable" nominees. Having Leahy vote Yes in particular gets the Dems out of the "knee-jerk opposition" accusation. Feingold and Kohl have not been active on the Committee and are not as beholden to the moonbat interest groups as the others are, so it was logical to assign them the token yes votes. Has nothing to do with their constituents at all. They were told how to vote.
I'm not entirely convinced he lost the state of Wisconsin. The margin was very close - certainly within the margin of democrat vote fraud in Milwaukee.