As Kellyanne Conway explained in an interview with the UK's "Channel 4" news that aired Monday,
Trump is shown trailing Clinton in most polls because his supporters aren't telling pollsters their true preference.
"It's become socially desirable -- especially if you're a college-educated person in the United States of America -- to say that you're against Donald Trump.
"The hidden Trump vote in this country is a very significant proposition," she said.
Conway told CNN Wednesday that interview was conducted weeks ago before she was named campaign manager.
And Conway -- a veteran pollster who previously worked on Ted Cruz's presidential campaign and for Trump's VP pick Mike Pence -- suggested that the campaign's internal data was more favorable than most polls show.
"Have you been able to put a number on" those particular voters, asked Matt Frei, the interviewer.
"Yes," Conway replied.
"What do you think it is?"
"I can't discuss it."
"Oh come on," Frei interjected.
But Conway declined. "No, it's a project we're doing internally. I call it the undercover Trump voter, but it's real."
Trump's campaign manager also criticized the media for presenting a skewed picture of the 2016 race.
"Just the cherry-picked polling numbers that are put out there by media outlets that are also bent on his destruction. Donald Trump performs consistently better in online polling, where a human being is not talking to another human being about what he or she may do in the election," Conway said.
Trump has also employed a version of this argument. Last week, he sent out a tweet that read, "They will soon be calling me MR. BREXIT!" It was a reference to the vote by the United Kingdom to leave the European Union -- the result of a referendum that many observers expected to go the other way but which polling showed to be close. Nevertheless, the Brexit vote has become a talking point for those who question the accuracy of polls of the 2016 presidential election.
Nigel Farage, a leader of the Brexit movement, told Sky News
that he would appear on stage with Trump on Wednesday. CNN has reached out to confirm the visit from Farage but has not yet received a response.
The idea that a significant portion of Trump voters are disguising their support to pollsters because they are embarrassed or afraid to admit it isn't backed up by much evidence. But it's the latest example in a long history of trailing candidates taking shots at unfavorable polls.
As founder of FiveThirtyEight Nate Silver pointed out on Twitter, 1984 Democratic nominee Walter Mondale also sought to discredit his poor polling by pointing to the size of his rallies and the enthusiasm of his supporters -- an argument frequently made by Trump surrogates -- only to lose the election by 18 points.
In CNN's latest poll of polls -- an average of multiple polls that meet CNN's standards -- Clinton leads Trump by 10 points.