At FiveThirtyEight, By Harry Enten and Dhrumil Mehta write:
This year was different from other wave years because of the unusually strong influence of the presidential vote in individual states in the last two cycles. It explained over 75 percent of the variation in results across the races this year. That’s the highest ever.
When controlling for the presidential vote, incumbency had 40 percent of the explanatory power it normally does. While it would be tempting to assert that incumbency doesn’t matter as much as it used to, it would also be wrong. In 2012, controlling for the presidential vote, the explanatory power of incumbency pretty much matched the historical average from 1982 to 2014.
In other words, negative feelings towards President Obama almost entirely overwhelmed the incumbency advantage in 2014. That’s why Democratic Sen. Mark Warner — a former popular governor who won his seat by 31 points in 2008 — nearly lost in Virginia even though Obama won the state twice. Republican Thom Tillis beat Democratic Sen. Kay Hagan in the purple state of North Carolina. And in Iowa, which has voted just once for a Republican presidential candidate since 1984, Republican Joni Ernst beat Democrat Bruce Braley.
They go on to mention candidate quality as another reason for the outcomes. Right after the election,
David Brooks surveyed the biographies of newly-elected GOP senators and governors:
Let’s pause over some of the institutions mentioned in these mini-bios: IBM, Reebok, the Red Cross, McKinsey and the Army. These are not fringe organizations. These are the pillars of American society.
Republicans won this election in part because they re-established their party’s traditional personality. The beau ideal of American Republicanism is the prudent business leader who is active in the community, active at church and fervently devoted to national defense.
