A year ago, Speaker Mike Johnson stood in front of a crowd of House Republicans chanting his name as if he were a championship quarterback.

Sleep-deprived after an overnight floor session, Mr. Johnson celebrated having rallied his party to pass its sweeping bill that cut taxes, slashed domestic spending and boosted immigration enforcement.

“Unified government — we did not want to waste that opportunity,” Mr. Johnson said.

But that is exactly what some House Republicans say has happened in recent months as the speaker has been forced to delay or scrap crucial agenda items because of resistance in his ranks, upending his efforts to accomplish critical tasks as the party tries to preserve its fragile majority in November’s midterm elections.

“The American people gave us Donald Trump and a unified Congress,” said Representative Troy Nehls, Republican of Texas. “We have both chambers, and we’re just wasting — we’re squandering time away.”

This week, Mr. Johnson could not even corral enough votes to bring up a celebratory resolution marking the first anniversary of the tax law, the biggest Republican policy victory of President Trump’s second term.

The collapse, which also derailed the annual defense policy bill with a pay raise for troops, was the coda to a two-week stretch in which Mr. Johnson lost control of the House floor to a rebellious group of hard-line Republicans.

As such episodes have grown more common, a key reason for them has come into sharper focus: Many Republicans are deeply frustrated with Mr. Johnson’s approach to governing with a razor-thin majority. When he finds himself in a bind, the speaker is quick to make big promises to disparate factions to get major bills across the finish line, only to reap the whirlwind from aggrieved members in his ranks when he struggles or fails to fulfill his vows.

Over the past year, Mr. Johnson repeatedly promised libertarian-minded conservatives that they would get a much-sought ban on central banks issuing digital currencies, only to have to kick the can down the road. His divergent deals with warring flanks of lawmakers over the gasoline blend E15 led to a bitter confrontation on the House floor that delayed and nearly derailed passage of the farm bill.

In early June, facing right-wing resistance to a $70 billion immigration enforcement bill, the speaker promised holdouts that, in exchange for their votes, he would bring long-sought border security legislation to the House floor by July 4. They voted yes, but the measure they wanted has not moved.

And for months, he has been telling another faction of restive Republicans that he would find a way to force action on Mr. Trump’s cherished voting restriction bill, which has passed the House but stalled in the Senate, where it has no viable path.

As a holiday recess approached this week, Republicans angry about the border security bill joined those irate about the lack of action on the elections bill. Together, they blocked the defense bill and a critical spending measure from coming to the House floor.

Representative Chip Roy, Republican of Texas, cited the promise to bring up the border bill. “That didn’t happen,” he said on Tuesday. “Let’s do what we need to do.”

With a dwindling number of days in session before the midterm elections, disgruntled Republican lawmakers left the Capitol on Tuesday afternoon, days before the nation’s 250th birthday celebration, with little to show for their efforts and a sense that they were frittering away their governing trifecta.

Mr. Johnson appeared to share those frustrations, telling reporters that some lawmakers “get very emotional about things, and sometimes they make irrational decisions.” He suggested their anger was misguided and better directed toward the Senate.

Yet he also maintained that the crackup was business as usual, given the party’s narrow majority.

“We have full control of the conference,” Mr. Johnson said. “This is the same thing we’ve been doing the whole time. We have the smallest margin in U.S. history.”

Previous speakers of both parties were typically able to hold lawmakers in line through fear or favors. But Republicans do not fear Mr. Johnson and have come to distrust his favors.

The risks of over-promising should be evident. Mr. Johnson became speaker after his predecessor, Kevin McCarthy, a California Republican, frustrated rank-and-file lawmakers by failing to deliver on his pledges, leading to his ouster.

Mr. Johnson is often seen haggling with lawmakers on the House floor during votes that stall for hours as he tries to win the necessary support.

Those conversations burst into shouted confrontations in April when Republicans tried to pass the farm bill. The speaker faced demands from farm state lawmakers seeking the year-round sale of E15, and from conservatives who opposed it. Both groups accused Mr. Johnson of reneging on deals.

“You had requests and demands on opposite sides of the conference that were literally irreconcilable,” Mr. Johnson said then. “If you meet one group’s demands, you can’t meet the other.”

His allies say that Mr. Johnson’s haggling may not yield quick-enough payoffs to avert crises like this week’s, but that it eventually produces results. The farm bill ultimately passed, as did separate ethanol legislation, they note. A temporary version of the digital currency ban made it into the housing bill now on Mr. Trump’s desk.

Mr. Trump has generally been Mr. Johnson’s most effective tool to bend lawmakers. But the limits of his reliance on the president became clear on Tuesday. Though Mr. Trump last week urged Republicans not to block their party’s bills, it was not enough to rally them behind Mr. Johnson.

That could be in part because the defectors were responding to Mr. Trump’s demands that Republicans do whatever is necessary to push through the stalled elections measure, which would impose nationwide requirements on voter identification and proof of citizenship, and severely restrict voting by mail. Far-right lawmakers have blockaded action in the House in an effort to force the Senate to act on that bill, which is being blocked by Democrats.

Mr. Johnson has tried to reassure that group, led by Representative Anna Paulina Luna of Florida, that Republicans can use a complicated legislative process called reconciliation, which allows budget-related bills to pass the Senate on a majority vote, to carry out Mr. Trump’s restrictions.

But reconciliation is governed by a set of rules that could make it difficult for the election restrictions to survive.

“It actually cannot be done on reconciliation,” Ms. Luna said this week. “And they know that.”

Mr. Johnson’s supporters have argued that any stumbles are inevitable given the size of his majority and its quarrelsome elements.

“When you are given an impossible task, you have to expect to fail from time to time,” said Representative Darrell Issa, Republican of California. “The fact that he has succeeded while dealing with impossible tasks more often than not represents a very good performance considering the hand he was dealt.”

But others contend that Mr. Johnson is in a situation of his own creation. Marjorie Taylor Greene, the former Republican congresswoman from Georgia, said in an interview that she had warned her colleagues not to trust Mr. Johnson.

She cited the speaker’s promise that Republicans would address the cost of health insurance premiums, something she argued he had yet to address.

“I told you so,” said Ms. Greene, who tried unsuccessfully in 2024 to remove Mr. Johnson. “I tried to get rid of the serial liar, but just like many other times, I was right and the G.O.P. conference was wrong.”

Olivia Diaz contributed reporting.