Andrew Yang qualifies for the next debate.

That didn’t stop the Buttigieg campaign from informing reporters that Mr. Johnson, who introduced Mr. Buttigieg as “the next president of the United States,” had “announced his support for him.”

Mr. Johnson said after the event that he’s still backing Ms. Klobuchar.

“They’re two good candidates,” he said. “I’m just happy with someone from the Midwest.”

Mr. Johnson said he was asked to introduce Mr. Buttigieg after the scheduled introducer had car trouble and missed the event. He called Mr. Buttigieg the next president, he said, because that’s just something you say when someone visits Iowa.

“It’s a courtesy,” he said. “I would do it for anyone who had a D behind their name.”

Despite his affection for them, Mr. Johnson doesn’t expect either Mr. Buttigieg or Ms. Klobuchar to win the state’s caucuses.

“My prediction is Senator Sanders,” he said, referring to Senator Bernie Sanders of Vermont, who is leading in the latest Iowa polling.

“There’s a lot of things that have happened, and Secretary Clinton didn’t do any good to tamp down his case,” he said, referencing critical remarks Hillary Clinton made last week about her former primary rival.

“I tell you, that guy’s people are going to be out there with a vengeance.”