“It is definitely embarrassing,” he said. “It’s a drag knowing there are people out there who are gloating.”

Jennifer Taub, a Vermont Law School professor who had become known for punchy anti-Trump columns with titles like “Yes, Collusion. Now What?” said, “There are definitely people who thought that Mueller would save us.”

Ms. Taub said she remained hopeful that Mr. Mueller’s full findings, which have not yet been made public, would somehow contradict the summary given by Mr. Barr. But she said she understands that the legal threshold for proving conspiracy is high.

Last week, she posted a picture of herself on Facebook lighting a candle with Mr. Mueller’s face on it. “I would hope that people who were in this cult of Mueller would have been self-aware or ironic,” she said on Monday.