In Politico’s insider poll of several dozen political professionals on both sides, 7 in 10 of the Republican pros believe that the polls are significantly undercounting support for Donald Trump. There are several reasons for this, most notably what pollsters call “social desirability bias,” which manifests itself as respondents telling pollsters they will vote one way while actually voting another way on election day.
How prevelant is this bias? Internal polling by campaigns can usually screen out most biases by asking the same questions several different ways. In media surveys, they aren’t quite as thorough, leaving open the possibility that there is a small but significant bias that goes undetected.
“I’m not sure how big a factor it is, but there is definitely a ‘Bradley effect’ going on out there,” said a Virginia Republican, referring to the African-American mayor of Los Angeles who led in polls but lost unexpectedly in the 1982 California gubernatorial race. “I personally know many Republicans that won’t admit that they are voting for Trump. I don’t like admitting it myself. It won’t matter if Hillary is up more than 5 points, but we might be in for a surprise if Hillary’s lead is less than 5 points on Election Day.”
A Michigan Republican — who, like all insiders, completed the survey anonymously —added that Trump voters are reticent to admit it publicly: “Anecdotally, that’s clearly the case in barber-shop conversations.”
A number of Republicans said that while they believe the polls are underestimating Trump, his deficit is too large for it to matter.
“He’ll outperform the polls but still won’t win,” a Pennsylvania Republican said.
“This form of survey bias is a common but marginal factor in many polls,” an Ohio Republican added.
For other Republicans, the “shy Trump” effect that might be deflating Trump’s support is less an issue than other sources of bias in the polls.
“I also believe that by polling likely voters rather than registered voters, polls are missing a lot of where Trump’s support lies,” an Iowa Republican said.
The phenomenon known as social desirability bias “may be part of it,” a Nevada Republican said. “I also think that the pollsters have not accounted for the uniqueness of this election and are not necessarily asking the right questions of the correct samples. Finally, many of the polls are deliberately slanted to suit the media’s political agenda. Taken all together, it’s almost impossible to know who is leading at this point.”
Some cited the energy of Trump supporters to suggest his backers are unforthcoming with pollsters.
“I see a lot of Trump signs on people’s lawns, plus a lot of anti-Clinton signs,” said a New Hampshire Republican.
But for a minority of Republicans, 29 percent, those hoping for a secret Trump vote to emerge on Election Day will be disappointed.
Trump would have to outperform polls by a historical margin to have any chance of winning at this point. That doesn’t mean it can’t happen, but the likelihood of Trump overcoming Clinton leads in swing states like Virginia, Michigan, and Wisconsin is slim.
Where this bias may make a positive difference is in red states like Arizona, Texas, and North Carolina, where the race is very tight, and battleground states like Nevada and possibly Pennsylvania, where a difference of two or three percentage points might put Trump over the top.
What isn’t taken into account in these calculations is the massive GOTV effort by the Clinton campaign. Clinton’s ground game dwarfs that of Trump in all battleground states and even states like Arizona and North Carolina. Trump may have a lot of secret supporters, but will they go to the polls and vote?
On that question hinges the election.