...probably not who you think. The real Democratic winner on Tuesday was Jim Doyle. Not only did he take down Peg Lautenschlager, the only prominent Democrat left in Wisconsin who was willing to stand up to him, but Steve Kagen's win in the 8th CD also neutralized what was potentially a huge drain on Doyle's ability to fundraise for the general election. Kagen is quite wealthy, and will largely self-fund his race against John Gard, freeing up millions of dollars to go into other hot contests like, for instance, the governor's race.
And the big losers on Tuesday were Wisconsin progressives, because Peg's loss eliminated the only effective opposition to Doyle within the Democratic party of Wisconsin. Which isn't to say that Kathleen Falk isn't a progressive, but it's very unlikely she'll bite the hand that feeds her by challenging Doyle in any meaningful way.
Politics is the intersection of self-interest and power. It's like a huge game of chess using live pieces, and politicians move those pieces to their advantage. Jim Doyle has shown once again that he's a master at this game. The problem, of course, is that the interests of the people at the top of the party don't always coincide with the interests of the party as a whole.
This primary was a classic example.