Mr. Trump reposted a Twitter message that said “Time to #FireFauci” as he rejected criticism of his slow initial response to the pandemic that has now killed more than 22,000 people in the United States. The president privately has been irritated at times with Dr. Fauci, but the Twitter post was the most explicit he has been in letting that show publicly.

The message Mr. Trump retweeted came from a former Republican congressional candidate. “Fauci is now saying that had Trump listened to the medical experts earlier he could’ve saved more lives,” said the tweet by DeAnna Lorraine, who got less than 2 percent of the vote in an open primary against Speaker Nancy Pelosi last month. “Fauci was telling people on February 29th that there was nothing to worry about and it posed no threat to the US at large. Time to #Fire Fauci.”…

Dr. Fauci has become a celebrated figure among much of the public, which trusts him far more than Mr. Trump, according to polls. A Quinnipiac University survey last week found that 78 percent of Americans approved of Dr. Fauci’s handling of the crisis compared with 46 percent who approved of the president’s response. That has prompted resentment among other government officials, some of whom have privately criticized Dr. Fauci for playing to the media and not always sending consistent messages.