An enduring mystery of the 2012 election cycle is how GOP candidates managed to lose senate races in both Montana and North Dakota, states which voted resoundingly for Mitt Romney–by 13.5 and 19.8 percentage points, respectively. Though pre-election polling data was relatively scant, statistician extraordinaire Nate Silver pegged the likelihood of a Republican victory in North Dakota at 92.5% and in Montana at 65.6%. Instead, Democrat Heidi Heitkamp prevailed over Rick Berg by 1.0% to replace the retiring Kent Conrad, while Democrat Jon Tester–long regarded the cycle’s most vulnerable incumbent–defeated Denny Rehberg by 3.9%.
Post-election analyses have generally cited demographic trends as a prime hurdle for Republicans, but such explanations would appear inapplicable to these races. An analysis  (PDF) by the Winston Group, a Republican polling outfit, flags the two outcomes as particularly troubling signs for the party because they cast doubt on popular explanations for why the GOP floundered. Relative to the rest of the country, the “Big Sky” region is old and white; the percentage of young voters actually decreased by 7% in Montana between 2008 and 2012. Such factors would seem to work in Republicans’ favor.
Neither Berg nor Rehberg held particularly “extreme” views by his state’s standards, and neither were unexpected victors in heated primary contests, i.e. Todd Akin or Richard Mourdock. Rehberg, who lost to Tester, had represented Montana’s at-large House district since 2001; Berg had represented North Dakota’s at-large House district since 2011–both were the “establishment” choices. Neither candidate attracted national attention for controversial remarks i.e. Akin or Mourdock, and were known commodities in their state.
And yet Berg underperformed Romney by 9.2%, while Rehberg underperformed Romney by 10.5%. Thus, a significant portion of voters in these states “pulled a switcheroo,” opting for Romney plus a Democratic senate candidate.
An inference to be made here is that while Obama was sufficiently unpopular in “Big Sky” country that Romney won easy victories, this dynamic did not translate into broad-based support for Republicans. In other words, many voters sought to signal their discontent with Obama, but not necessarily re-empower the Republican Party. It seems unlikely that a different tack on immigration policy, one widely-suggested post-election remedy, would alleviate the party’s woes in Montana or North Dakota. Rather, for a host of reasons, conservatives in these states have soured on the national GOP’s brand.