An analysis by The New York Times found over 70 accounts on Twitter that have promoted the hashtag #FauciFraud, with some tweeting as frequently as 795 times a day. The anti-Fauci sentiment is being reinforced by posts from Tom Fitton, the president of Judicial Watch, a conservative group; Bill Mitchell, host of the far-right online talk show “YourVoice America”; and other outspoken Trump supporters such as Shiva Ayyadurai, who has falsely claimed to be the inventor of email.

Many of the anti-Fauci posts, some of which pointed to a seven-year-old email that Dr. Fauci had sent praising Hillary Clinton when she was secretary of State, have been retweeted thousands of times. On YouTube, conspiracy-theory videos about Dr. Fauci have racked up hundreds of thousands of views in the past week. In private Facebook groups, posts disparaging him have also been shared hundreds of times and liked by thousands of people, according to the Times analysis.

One anti-Fauci tweet on Tuesday said, “Sorry liberals but we don’t trust Dr. Anthony Fauci.”

The torrent of falsehoods aimed at discrediting Dr. Fauci is another example of the hyperpartisan information flow that has driven a wedge into the way Americans think. For the past few years, far-right supporters of President Trump have regularly vilified those whom they see as opposing him. Even so, the campaign against Dr. Fauci stands out because he is one of the world’s leading infectious disease experts and a member of Mr. Trump’s virus task force, and it is unfolding as the government battles a pathogen that is rapidly spreading in the United States.

It is the latest twist in the ebb and flow of right-wing punditry that for weeks echoed Mr. Trump in minimizing the threat posed by the coronavirus and arguably undercut efforts to alert the public of its dangers. When the president took a more assertive posture against the outbreak, conservative outlets shifted, too — but now accuse Democrats and journalists of trying to use the pandemic to damage Mr. Trump politically.