Well, let’s break that down. As you pointed out, the LP typically gets about 1% every election cycle, so we can set that aside as a baseline. So we’d be looking at the outlier that seemed to be unique to 2016, or about 2.27% of his numbers up for grabs in regard to any swing toward Johnson. Do we have any indication as to the breakdown of his support? There is this from November 26 from
CNN:
It's impossible to know how an election could have gone under hypothetical scenarios, but the Johnson campaign regularly said they thought they were pulling support equally from would-be Trump supporters and would-be Clinton voters. Stein's campaign, meanwhile, made a constant, explicit appeal to disenchanted Democrats and former supporters of Vermont Sen. Bernie Sanders.
If Johnson and Stein weren't in the race, it's also possible many of their supporters may have stayed home. But if about half of Johnson's supporters would have voted for Clinton over Trump, and if most of Stein's supporters broke for the Democrats, the electoral map would have been decidedly different.
And there was this from
FiveThirtyEight back in July of 2016 (i.e., long before the election, but still relevant to this question):
The majority of pollsters (12) have Clinton’s margin over Trump shrinking when at least one third-party candidate is included. The difference in margins, however, varies among pollsters, and a few, such as Ipsos, have Clinton’s lead rising by the tiniest of bits when at least Johnson is included. Overall, including third-party candidates takes about 1 percentage point away from Clinton’s margin, on average.
We can argue about the significance of a single percentage point. It’s not a very big deal when Clinton is leading by 5.5 percentage points in the FiveThirtyEight national polling average and is projected to win the national vote by 6.3 percentage points in the FiveThirtyEight polls-only model. (Note that our model prefers the versions of polls that include Johnson. Otherwise, Clinton’s advantage would be slightly larger.1) The discrepancy could, however, become an issue if the race becomes tighter.
...
Johnson looks especially likely to peel votes from Clinton and Trump because he will probably achieve ballot access in all 50 states, which is unusual for a non-major-party candidate.
And then there was this from CNN in
August of 2016:
Way down in the crosstabs of CNN's latest presidential poll, we learn how voters who preferred Bernie Sanders to Hillary Clinton say they're most likely to vote in November. A clear majority, 69 percent, favor Clinton. Jill Stein of the Green Party is in second place, with 13 percent. Gary Johnson of the Libertarian Party is third, at 10 percent. Donald Trump brings up the rear, with just three percent of the total—the same as "other."
If we use the numbers from the primaries as an indication of how many Sanders supporters there were, then we’re talking about 10% of 13 million or 1.3 million Sanders’ supporters potentially throwing their votes away on a third party as a protest against Clinton, and about half that would go to Johnson, or around 650,000 votes. That’s just from the Sanders’ supporters. Harder to discern would be among “independents” or other undecided Dems that got swayed by the Comey effect (or racism/sexism).
So, iow, yes,
there is definitively evidence indicating that votes that would have otherwise gone to Clinton went instead to Johnson (and not necessarily at Trump’s expense).
