It's medium red
WI-6 has 3 counties that voted for Obama in 2012: Columbia, Marquette, and Winnebago. Not all of Winnebago is in WI-6, but the part that isn't is pretty Republican. Obama won Columbia by about 4000 votes, Winnebago by about 3000 votes, and Marquette by a whopping 22 votes (Marquette is tiny). I suspect the part of Winnebago cut off was intentionally selected to send some Republicans to WI-8 since they'd be needed more there.
It also has 4 entire counties that voted for McCain in 2008: Fon du Lac, Sheboygan, Green Lake, and Ozaukee. Romney won these 4 by a combined roughly 33,000 votes and it's hard to imagine either Fon du Lac or Ozaukee being won by the Democrat absent a scandal (and even then Ozaukee probably wouldn't). Part of Dodge County, which was won by McCain, is also in this district. Bill Clinton won Sheboygan County in the 1996 blowout, but that was a long time ago.
This leaves Waushara and Manitowoc Counties as the only others in the district (plus a tiny sliver of Milwaukee County with some of the more Republican North Shore suburbs), both of which were won by Romney (by a substantial margin in the case of Waushara). Manitowoc could conceivably give the right Democrat a good margin of victory. A blue collar moderate type could do very well here and could probably keep Sheboygan respectably close, but it would be hard for the Democrats to win.
In any case, Grothman has a huge uphill battle to climb in the primary because his only base would be Ozaukee County. A Republican from Sheboygan, Fon du Lac, Oshkosh, or Manitowoc would have a much easier road through the primary. I suspect with Grothman it's still Likely R and Safe R without him.
East Central WI is a part of the state where McCain did much worse than Romney and was something of an aberration (see Green Bay as well).
