The third-party vote is unusually big this year — bigger than in any presidential election since 1992. Libertarian nominee Gary Johnson and Green Party nominee Jill Stein regularly combine for more than 10 percent of the vote in national polls. But despite those relatively strong showings, we know little about the partisan makeup of Johnson’s and Stein’s voters; there are enough of them to be worth tracking but too few to make up a meaningful sample in most individual surveys. Which party these voters favor outside of the presidential race could affect down-ballot races for the U.S. Senate and House.
We can learn a bit more about these voters from new data that Morning Consult has shared with FiveThirtyEight; it’s aggregated from the firm’s national tracking polls from Aug. 1 through Aug. 20. Johnson’s voters are very slightly more favorably disposed toward Republicans. Stein’s voters are overwhelmingly more favorable toward Democrats. If these voters shun the two major parties at the top of the ticket but choose between the two in down-ballot races, they could help Democrats in congressional races.
When respondents were asked which party’s candidate they would back in their district’s U.S. House race, only 53 percent of Johnson backers said the Republican; 46 percent said they would vote for the Democrat. (They were not offered the option of a third-party candidate.)1 That’s a bit surprising — I would guess that a Libertarian candidate would draw support disproportionately from the GOP. But the small Republican edge among Johnson supporters means that, as a group, they would barely affect down-ballot races if they voted for a major-party nominee. Considering that 9 percent of all voters in the Morning Consult data said they were supporting Johnson for president, the 7-point edge in the U.S. House question means that Johnson voters are adding a little less than two-thirds of a percentage point of support to the Republican margin in the national House vote.
Stein supporters, meanwhile, overwhelmingly favor Democratic House candidates (not surprisingly). Democrats win the House ballot among Stein voters 74 percent to 25 percent. That nearly 50-point margin means that although just 4 percent of all voters are backing Stein, they add 2 percentage points to the aggregate Democratic margin in House races.
Adding together the Johnson and Stein voters creates a group that is slightly more Democratic-leaning than the electorate as a whole. By an 11-point margin, these third-party voters prefer the Democratic candidate for Congress.2 Among Donald Trump and Hillary Clinton voters only, Democrats lead the aggregate House vote by 7 points. If Johnson and Stein supporters vote for a major-party candidate for the U.S. House, the Democrats’ overall margin would grow by about 1 percentage point relative to where it would be if they favored independent candidates in down-ballot races too. (And that makes sense: In July, I found that the Democratic presidential candidate’s margin over the Republican increases by about 1 point when third-party voters are forced to choose between one of the two major-party nominees.)
Now, I should note that the Democrats are unlikely to retake the House. While the national house ballot has historically had a strong correlation with the eventual popular vote in the House, it’s not perfect. A seat-by-seat analysis indicates that Democrats will probably not gain enough seats to take control of the chamber. What’s important to note here is that third-party voters are more inclined to vote Democratic than the nation as a whole.
Of course, I’m not sure it’s fair to expect that most of these third-party presidential voters will choose a Democrat or Republican for the U.S. House or Senate. Keep in mind that Morning Consult didn’t give respondents the option to choose an independent candidate, an option that Johnson and Stein voters will have in November.
It’s reasonable to think that some Johnson and Stein supporters will vote for major-party candidates in down-ballot races — Clinton’s and Trump’s historically high unfavorable ratings are likely driving some voters who typically choose one of the two major parties to look elsewhere. But 31 percent of Johnson voters and 30 percent of Stein voters initially said3 that they were undecided on whether they would vote for the Republican or Democratic candidate in their House race. That suggests to me a hesitancy among these voters when they are presented with only the two major parties as options. Only 13 percent of Trump voters and 9 percent of Clinton voters said they were undecided.
Still, the Morning Consult data suggests that Democrats would be wise to appeal to Johnson and Stein voters in House and Senate races.