In Cleveland County, Okla., the chairman of the local Republican Party openly wondered “why violence is unacceptable,” just hours before a mob stormed the U.S. Capitol last week. “What the crap do you think the American revolution was?” he posted on Facebook. “A game of friggin pattycake?”

Two days later, the Republican chairman of Nye County in Nevada posted a conspiracy-theory-filled letter on the local committee website, accusing Vice President Mike Pence of treason and calling the rioting a “staged event meant to blame Trump supporters.”

And this week in Virginia, Amanda Chase, a two-term Republican state senator running for governor, maintained that President Trump might still be sworn into a second term on Jan. 20 and that Republicans who blocked that “alternative plan” would be punished by the president’s supporters.

“They’ve got Mitch McConnell up there selling out the Republican Party,” Ms. Chase, who spoke at the protest in Washington last week, said in an interview. “The insurrection is actually the deep state with the politicians working against the people to overthrow our government.”

As Mr. Trump prepares to exit the White House and face a second impeachment trial in the Senate, his ideas continue to exert a gravitational pull in Republican circles across the country. The falsehoods, white nationalism and baseless conspiracy theories he peddled for four years have become ingrained at the grass-roots level of the party, embraced by activists, local leaders and elected officials even as a handful of Republicans in Congress break with the president in the final hour.

Interviews with more than 40 Republican state and local leaders conducted after the siege at the Capitol show that a vocal wing of the party maintains an almost-religious devotion to the president, and that these supporters don’t hold him responsible for the mob violence last week. The opposition to him emerging among some Republicans has only bolstered their support of him.

And while some Republican leaders and strategists are eager to dismiss these loyalists as a fringe element of their party, many of them hold influential roles at the state and local level. These local officials are not only the conduits between voters and federal Republicans, but they also serve as the party’s next generation of higher-level elected officials, and would bring a devotion to Trumpism should they ascend to Washington.

The continued support for the president is likely to maintain Mr. Trump’s influence long after he leaves office. That could hamper the ability of the party to unify and reshape its agenda to help woo back moderate suburban voters who play a decisive role in winning battleground states and presidential elections.

At the same time, stepping away from the president could cost the party his supporters — millions of new working-class voters who helped Mr. Trump capture more votes than any other Republican presidential candidate in history.

“It is priority No. 1 to retain Trump voters,” said Harmeet Dhillon, an R.N.C. member from California. “There is no way to do that with rapid change, tacking in a different direction. Voters are looking to the party for continuity and to stay the course.”

An Axios-Ipsos poll released Thursday showed that a majority of Republicans support the president’s recent behavior and say he should be the Republican nominee in 2024.

Already, some from the Trump wing are threatening primary challenges to Republicans deemed insufficiently loyal to the president and fierce opposition to any Republican who works with the new Biden administration. With Mr. Trump barred from prominent social media platforms, they’re immersing themselves in right-wing media outlets and waiting for new conservative social media platforms many say are being set up.

“The party is definitely with Trump,” said Debbie Dooley, a conservative activist in Georgia. “I’m seeing anger but it’s kind of nuanced. There are people that are angrier at these Republicans that have turned their backs on Trump than they are at Democrats.”

That was evident shortly after 10 Republicans joined with Democrats to support impeachment on Wednesday. Within hours of the vote, Drew McKissick, the chairman of the South Carolina Republican Party, blasted out a statement attacking Representative Tom Rice, a Republican from his state who had backed impeachment.

“We completely disagree with this sham and to say I’m severely disappointed in Congressman Tom Rice would be an understatement,” Mr. McKissick said.

Several House Republicans also called for Representative Liz Cheney of Wyoming, a high-profile voice for impeachment, to step down from her leadership position in the party’s caucus.

Anthony Sabatini, a Florida state representative, described Ms. Cheney and other Republicans who voted for impeachment as “artifacts,” saying they were out of step in a party that has embraced a more populist platform opposed to foreign interventions and skeptical of free trade.

“She’s like a fossil,” he said of Ms. Cheney. “The party is completely and totally realigned. Mitt Romney wouldn’t win in a primary today. He would not be able to be elected dogcatcher today.”

For years, opponents to Mr. Trump argued that he would lose his hold on the party after a devastating event — like unrest or violence that would shock the nation. Last week’s breach of the Capitol appears to have presented that opportunity to Republicans who want to refocus the party around Mr. Trump’s policies, and dispense with the polarizing language and divisive actions that marked his four years in office.

“In this world, I think there’s lots of room for the Republican Party,” said Juliana Bergeron, an R.N.C. member from New Hampshire. “I’m not sure there’s room for the Republican Party of Donald Trump.”

But for many grass-roots officials, the episode at the Capitol was not the inflection point that some Republicans in Washington assumed it would be.

“No, Trump does not have any blame, but the Democrats certainly do, along with all the Republicans that follow with them,” said Billy Long, the Republican Party chairman in Bayfield County, Wis., who said he was planning to break away from the G.O.P. to start a local Trump-centric third party. “The Trump movement is not over; like Trump said himself, we are just getting started.”

Republican voters, too, have largely drawn a sharp distinction between the president and those who stormed the Capitol, with 80 percent saying they do not hold Mr. Trump responsible for the rioting and 73 percent saying he is protecting democracy, according to polling released by Quinnipiac University this week.

Even in blue states, Republican leaders find themselves still grappling with Mr. Trump’s politics of grievance. In the New Jersey State Senate, Republicans were split on a resolution condemning Mr. Trump for inciting the crowd that attacked the Capitol. The majority of Republicans chose to abstain, and many used their time on the floor to try to flip the debate to the protests against racial injustice over the summer, and had to be reprimanded by the Senate president for veering off topic.

Even if Mr. Trump fades from political life, losing his social media megaphone and bully pulpit, his supporters say his message will be carried forward by a party remade in his image and with strong structural support at all levels.

Since Mr. Trump’s 2016 victory, 91 of the 168 positions on the Republican National Committee have turned over, with virtually all of the newcomers elected by Trump-aligned state parties.

The president received widespread praise at a national party meeting held two days after the siege, and was greeted with applause when he called into a breakfast gathering.

Already, battle lines are being drawn between the Trump wing and those who would like to move past the president.

Efforts to mount primary challenges to incumbent Republicans are underway in several states, with the encouragement of Mr. Trump. In Georgia, potential primary candidates are reaching out to conservative activists about challenging the Republican governor, lieutenant governor and secretary of state. Other targets may include Gov. Mike DeWine of Ohio and Senators Lisa Murkowski of Alaska and John Thune of South Dakota.

“The election was crooked and Republicans who could have done something did very little,” said Dave Wesener, the chairman of the Republican Party in Crawford County, Wis. “Those Republicans who have not been supportive I affectionately call RINOs. All RINOs should be primaried by conservatives.”

Mr. Wesener plans to give up his role in the local Republican Party next month to demonstrate his disappointment that the party did not fight harder to overturn the results of the election. He also plans to give up his Green Bay Packers season tickets, to protest the team’s painting of racial justice slogans on its home field.

In Virginia, Ms. Chase is likely to face a multicandidate Republican field for governor, which will be decided at a convention of party activists this summer. Though state G.O.P. officials opted to avoid a primary in hopes of denying Ms. Chase their nomination at a convention, the party’s activist base is filled with Mr. Trump’s most die-hard supporters.

“I’ve been called Trump in heels,” Ms. Chase said. “The regular grass roots of Virginia who are not part of the Republican establishment elite, they’re supporting me.”

The siege at the Capitol last week has drawn an even brighter line dividing the party. State legislators from more than a dozen states attended the protest, with at least one facing criminal charges for breaching the Capitol as part of the riot. Meshawn Maddock, an activist who is poised to be the incoming Michigan Republican Party co-chairwoman, helped organize busloads of supporters from her state to travel to the Capitol. In the days after the violence, she joined a conservative online group where some participants openly discussed civil war and martial law.

Many continue to defend their role in the event.

“Those who hold sway in Congress today look out on much of the country with disdain. Trump has never done that,” said State Representative David Eastman of Alaska, who attended the protest. “I, along with nearly a million other Americans, was glad to travel to D.C. to hear the president speak and thank him for his four years in office. Those in today’s ruling class will never truly understand why.”

Nick Corasaniti contributed reporting.