What Is the Coattail Effect? Presidential Popularity and Down-Ballot Performance

The coattail effect describes the tendency of a popular top-of-ticket candidate — most commonly a presidential candidate — to boost the electoral performance of their party’s down-ballot candidates. The image is of candidates clinging to a popular figure’s coattails and being carried to victory alongside them.

The effect works through several mechanisms. First, a popular presidential candidate drives higher turnout among base voters, who also cast votes down the ballot. Second, voters who are strongly motivated by the top candidate often vote a straight party ticket, benefiting all of the party’s nominees. Third, in wave elections, the winning party’s enthusiasm can carry relatively weak or unknown candidates to victory in districts they would normally lose.

The coattail effect is strongest in presidential election years when turnout is highest and partisan cues are most salient. It is weakest — or runs in reverse — during midterm elections, when lower turnout tends to favor the opposition party and the party in the White House typically loses seats.

The 2018 midterms illustrated what political scientists call the “negative coattail” effect — when an unpopular president drives opposition turnout and enthusiasm, costing their party seats. President Trump’s approval ratings averaged around 40-42% heading into the midterms, well below the ~50% threshold that tends to protect a party in the midterms.

Democrats gained 40 House seats and won the majority, flipping competitive suburban districts in Pennsylvania, Virginia, Texas, Georgia, and California that Republicans had held for years. The suburban shift was particularly notable: college-educated suburban voters — especially women — moved strongly toward Democrats. Democratic candidates also won 7 governorships and hundreds of state legislative seats.

The 2018 result set the stage for the 2020 redistricting cycle, as Democrats gained control of more state legislatures and could influence post-census map-drawing.