“We think there’s a big hidden Trump vote in this country,” said Kellyanne Conway, campaign manager for Republican presidential nominee Donald Trump, who is gaining in polls against Democratic rival Hillary Clinton.
Many Trump supporters do not trust polls or pollsters. But there could be another reason why they don't identify themselves: To some, Trump voters have a bad reputation.
Democratic presidential candidate Hillary Clinton put some of his supporters in what she called a "basket of deplorables."
Many people don't want to be put in that basket. So if someone asks who they are voting for, they may keep quiet about it. "They'll go ahead and vote for that candidate in the privacy of a [voting] booth," says Dartmouth College political science professor Joe Bafumi. "But they won't admit to voting for that candidate to somebody who's calling them for a poll."
Something similar happened in the 1980s to Tom Bradley, the first African American to run for governor of California. He had a big lead in the polls, but lost the election.
"Many people argue it was because there were a lot of white Democrats who said that they were going to vote Democratic," Bafumi says. "But when it came time to go to the polls, they didn't vote for Bradley because he was black. "
What became known as the "Bradley effect" seemed to have disappeared from American politics by Barack Obama's presidential candidacy in 2008. But some analysts see a "reverse Bradley effect" for Trump early in the race.
If people weren't telling pollsters about their true intentions during the primaries, "there really is not strong support to suggest that that's going on in the general election," says Courtney Kennedy, head of survey research at the Pew Research Center. If the effect were significant, it should have been evident when voters actually went to cast their ballots during the primaries. It wasn't.
"He was basically evenly split in terms of overperforming and underperforming where his polls were."
According to Princeton University Election Consortium founder Sam Wang, "It looks like many of those undecideds are people who can't quite bring themselves to vote for Donald Trump who normally vote Republican."
"Really, the thing that probably is going to decide this election is which campaign is better able to get those people to actually show up on election day.”