The standard deviation of GOP Senate candidate overperformance (or underperformance) over Mitt Romney in the two-party vote in 2012 is 7.3 percentage points. Thus, you get absurdities like a Democrat winning a Senate seat in North Dakota, a state that hasn’t voted for a Democratic presidential candidate since 1964. The standard deviation of Mitt’s performance in the two-party vote among the states that had Senate races is only a slightly larger 11.08 points. Considering the Republican presidential two-party vote only fell by about 5 points between 2004 and 2008, and that there was a YUGE (certainly more than one SD in size) deterioration in the approval rating of GWB between 2004 and 2008, it can be ascertained with fair reason that no matter how badly Trump performs, even if it’s as bad as McSame, candidate quality will matter more in this year’s Senate contests than anything Trump did.
People should understand that.