By Jim Ellis
Dec. 13, 2018 — Reviewing documentation from the 2018 US Senate races, it appears there is at least a tangential correlation between an incumbent senator’s pre-campaign approval rating and the vote percentage garnered on Election Day.The Morning Consult public affairs firm routinely surveys senators and governors to produce approval indexes for every member. Their 3rd Quarter 2018 sampling was publicly released on Oct. 10, one month before the election and just at the beginning of prime time campaigning.
Looking at the 32 incumbent senators who were on the ballot in November, the mean average increase from the individual’s approval score to the final vote percentage is 9.6 points when using the Morning Consult favorability index as our constant and the median is nine points.
The senator dropping the furthest from approval to vote percentage, down five points, was Maine Sen. Angus King (I), but the number is a bit deceiving. King scored a 58 percent positive approval rating in mid-October, but only received 53 percent in the election. Because the senator is an Independent and the Democrats with whom he caucuses did file their own candidate, the next closest opponent scored 35 percent. Therefore, his political standing still proved strong.
On the other end of the spectrum, the senator who improved the most from an upside-down favorability index rating to the vote was New Jersey Sen. Bob Menendez (D). While his October index was a poor 31:46 percent favorable to unfavorable, the worst by far among the 32 senators standing for re-election, he was successfully re-elected, 54-43 percent, over retired pharmaceutical company CEO Bob Hugin (R).
The upswing is partially due to a strong ideological campaign message, but the more plausible reason for Menendez’s stark improvement was President Trump’s standing within the state. In a pre-election poll from Monmouth University, respondents were asked if their vote for a New Jersey senator would be more about incumbent Bob Menendez or President Donald Trump. An overwhelming 72 percent said their Senate vote would be more about Trump than the actual person for whom most voted.
Of note, the eight senators who scored a 50 percent or greater approval score were all re-elected, but one, Montana Sen. Jon Tester (D), saw his vote percentage drop below his early October approval rating and ended in a close election. The remaining seven senators with majority approval in early October all won easily.
The Big Sky Country electoral result suggests that Sen. Tester, who recorded a 52:37 percent favorability ratio before campaign prime time but won re-election with just a 50-47 percent spread over state Auditor Matt Rosendale (R), lost support when the central campaign messages were delivered to voters in earnest and may have further dwindled in vote preference had the campaign lasted longer or the final push started earlier.
It is also interesting to compare the senator standing for re-election’s rating with that individual’s Senate partner who hails from the same state. In the 28 instances where a senator was standing for re-election in November while the state’s other senator was not, the in-cycle incumbent was viewed as the more popular in only 11 of the 28 instances.
The biggest difference between two senators sharing the same constituency, not surprisingly, came in New Jersey. With Sen. Menendez scoring a low 31:46 percent ratio, Sen. Cory Booker, the Garden State’s junior senator, posted an almost opposite 48:31 percent favorable to unfavorable score.
There also appears to be a direct correlation between the senators who lost re-election and their pre-campaign prime-time approval rating. Of the five senators who were defeated, three — Sens. Bill Nelson (FL), Claire McCaskill (MO), and Dean Heller (NV) — were found in upside-down approval territory in early October. Sen. Joe Donnelly (D-IN), while in positive space, only registered a 39:38 percent favorability index. This compares unfavorably to Indiana’s other senator, Republican Todd Young, who reported a 41:29 percent positive ratio.
Ironically, within the defeated group, the one posting the strongest approval score in early October, North Dakota Sen. Heidi Heitkamp (D) at 47:43 percent positive to negative, actually lost by the largest election spread, 55-44 percent. But, this can largely be attributed to a series of negative campaign moves and decisions, such as the senator’s vote against Supreme Court Justice Brett Kavanaugh, and making a major mistake with regard to exposing a victim of sexual assault in a campaign ad.