Wisconsin is too polarized for Johnson to lose by more than 10. Nice try, though.
Senate 2000, 2004, and 2006 beg to differ. Tommy Thompson won three of his five elections by over ten percent.
That was pre-Obama/Tea Party movement. The country was less polarized then.
And Thompson (back then) was not Johnson.
I will also add that the 2004 Senate race had a nasty, divisive Republican primary between several weak candidates. And the Repjublican candidates against Kohl in 1994, 2000, and 2006 were not serious. I don't know why the Republicans never put up any (real) candidate against Kohl.
Because he was well liked and couldn't be beaten. He won every county in the state in 2006.
A serious, well-known, moderate Republican would have probably beat him in 1994. It also helps that 2006 was a massive Democratic wave. I will also note that looking at RCP, it was around this time of the year in 2012 when Tommy Thompson's small but consistent lead died, and Baldwin took the lead.