While Ryan certainly won't win by the margins he's won in the past since he's now in the national spotlight, I would assume he would be safe even if Obama carries WI-1, no?
He might. Ryan is now seen as a "national" leader. A lot of people, including Obama fans, want a national leader to cater to their local interests.
Being a national leader sure didnt help Tom Foley or Tom Daschle.
Nevertheless, Ryan is probably safe in all but a very bad GOP midterm where Democrats put up a decent challenger.
In a special election early in a Romney administration, Democrats would have a good shot at picking the seat up. It was carried by Russ Feingold by two points in 2004.