WAUKESHA, Wisc. — While seeking to publicize his success in unscientific online polls after the presidential debate on Monday, Donald J. Trump on Wednesday promoted an unsubstantiated and debunked conspiracy theory about Google suppressing negative news in search results about his opponent.

“The Google poll has us leading Hillary Clinton by two points nationwide, and that’s despite the fact that Google search engine was suppressing the bad news about Hillary Clinton,” Mr. Trump told a crowd here, referring to an Independent Journal Review-Google Consumer Surveys poll. “How about that?”

The conspiracy theory began with a video from the online outlet SourceFed that went viral this year, and quickly garnered headlines on conservative news sites like Breitbart and Infowars.

The video featured someone selectively testing Google’s autocorrect feature, claiming that it was not showing results like “Hillary Clinton criminal” when “Hillary Clinton cr,” was typed in, while other search engines, like Bing, returned different results.