“Wikileaks also shows how John Podesta rigged the polls by oversampling Democrats, a voter suppression technique,” Trump began at a rally on Monday, referring to Hillary Clinton's campaign manager. “And that's happening to me all the time. When the polls are even, when they leave them alone and do them properly, I'm leading. But you see these polls where they're polling Democrats. How's Trump doing? Oh, he's down. They're polling Democrats!”
Then Trump referenced a hacked 2008 email from Democratic activist Tom Matzzie that references “oversampling,” a word which Trump supporters immediately took to mean “rigging” polls by adding disproportionate numbers of certain demographic groups.
“In an email, Podesta says that he wants oversamples for our polling in order to maximize what we get out of our media polling,” Trump said, reading the email in question from a teleprompter.
As many have noted, “oversampling” is a polling term which means polling enough members of certain political parties, genders, demographic groups, and others in order to get a statistically significant result for each group. These larger numbers are then weighted to their actual proportion in the population when the overall poll numbers are calculated.
In the hacked email, Matzzie also mentions “our poll” and “media polling”—signals that the discussion of oversampling is not about polls from media companies like the New York Times or Rasmussen, but instead about an internal poll intended to test a campaign's new advertising material.
It wouldn't make sense for Clinton consultants and allies to skew internal campaign polls, the accuracy of which the campaign relies on in order to make strategic decisions. But Trump didn’t seem to notice that as he read the email aloud in Florida.