Former Rep. Matt Gaetz, the Florida congressman turned attorney general turned baggage cable news host, made a bold proclamation at 9:46 a.m. on the opening day of the 119th Congress.

“Mike Johnson is elected speaker today,” Mr. Gaetz, who unseated the last Republican speaker, wrote on social media. “In the first vote. People may or may not like that. I’m just reporting the news.”

With potential holdouts pointing to a revolt against Mr Johnson, it seemed an overly optimistic statement about the fate of an embattled leader who commands a tiny majority. But in the end it turned out that Mr. Gaetz was well informed about the story.

Several hours and a lengthy roll call vote later — after six abstentions finally called Mr. Johnson’s name and President-elect Donald J. Trump called from his golf course in Florida to persuade two other defectors to switch votes — Mr. Johnson won the gavel.

The relief was clear on his worried face.

It felt like an appropriately shaky start to what is expected to be a turbulent Republican-majority Congress at the start of Mr. Trump’s second term.

As Mr. Johnson spent the morning huddled in his office near the Rotunda and chatting with objectors, the Capitol was filled with the energy of the first day of school.

On the Senate side, Vice President Kamala Harris arrived to swear in 100 senators, including political critics like Josh Hawley of Missouri and Bernie Moreno of Ohio, who chatted politely with the woman who blasted them just months ago for her “radical agenda.” had criticized.

A crowd of daughters who came with Dave McCormick, the Pennsylvania Republican who unseated Senator Bob Casey, the state’s longtime Democratic incumbent, stayed after he took his oath to take a group photo with Ms. Harris, and whispered and giggled with her before reluctantly walking away.

Back at the House of Representatives, former California Speaker Nancy Pelosi received a hero’s welcome in her first return to Washington since undergoing emergency hip surgery after stumbling on a marble staircase in Luxembourg. In a stunning move, Ms Pelosi had swapped her signature stilettos for cozy slip-on clogs.

She sat next to Representative Hakeem Jeffries, the Democratic leader from New York, who maintained a stoic expression throughout Mr. Johnson’s travails, as if to quietly signal that the turmoil unfolding on the floor was, as usual, by the Republicans.

As Rep. Ronny Jackson of Texas, who served as White House physician during Mr. Trump’s first term, received a new license plate and congressional membership pin earlier in the day, he said he had doubts about Mr. Johnson’s fate .

“Someone might have to do a protest vote or something to get it out of their system, but they better get it out of their system,” he said. “Trump can do a lot with executive orders, but the point is that we have to legislate.”

Amid all the drama and speculation, it was easy to forget that until the last Congress, the election of a speaker was little more than a formality. But as voting began Friday, it looked like House Republicans would repeat their performance from two years ago, when Rep. Kevin McCarthy needed 15 votes and four days to secure the gavel in a once-in-a-century contest Embarrassment of a ground fight.

Rep. Thomas Massie, Republican of Kentucky, voted in protest for Rep. Tom Emmer of Minnesota, the GOP politician, and then Rep. Ralph Norman of South Carolina shouted “Jim Jordan,” making it seem as if Mr. Johnson was losing the first round. Soon, Rep. Keith Self of Texas would join them in naming another person.

Grinding followed. The same was true of lashing-out phone calls from Mr. Trump, who was attacked at his golf course in Florida to twist the arms of some objectors.

Suddenly, typically disruptive members of Congress spoke up and tried to help close the deal. Rep. Marjorie Taylor Greene of Georgia, who tried to oust Mr. Johnson last year, had stopped by and was photographed speaking on the phone with Susie Wiles, the new White House chief of staff.

Rep. Nancy Mace of South Carolina, one of eight Republicans who voted to oust Mr. McCarthy last year, pulled the objectors into a private room so they could speak to Mr. Trump on speakerphone.

After inflicting a measure of humiliation on Mr. Johnson, Mr. Self and Mr. Norman finally turned around and allowed him to win the gavel on the first ballot — just as Mr. Gaetz had predicted.

Some Republicans tried to think positively.

“He did in one ballot what it took us 15 to do last time,” said Rep. Tom Cole, the veteran Republican from Oklahoma. “I think that’s a very good sign.”

But that is the beginning of the story, not the end. Members of the far-right House Freedom Caucus expressed in a letter their “sincere reservations about the speaker’s track record over the past 15 months.”

Mr. Trump was more optimistic.

“Mike will be a great speaker,” he wrote on social media, “and our country will be the beneficiary.”