DES MOINES — Far from Washington, and even farther from their home congressional districts, Representatives Matt Gaetz of Florida and Marjorie Taylor Greene of Georgia found their people.

As the two Republican lawmakers spoke at an “America First” rally in Des Moines, held in an auditorium that often hosts people with presidential aspirations, up was down and misinformation was gospel. Ms. Greene denounced Covid-19 vaccines to applause. Both declared former President Donald J. Trump the rightful winner of the 2020 election.

These were facts, argued Eric Riedinger of Des Moines, 62, a small-business owner who attended the event and owns the website BigTrumpFan.com. And he would not vote for any Republican who failed to state this clearly, he said.

“My biggest issue looking ahead: Stop the RINOs,” he said, using a pejorative conservative phrase for ‘Republicans in Name Only.’ “If they’re part of that infrastructure bill and supporting it, they’re not doing what they’re supposed to be doing.”

The fringe of the Republican Party is sick of being called the fringe. Led by people like Ms. Greene and Mr. Gaetz, two upstart members of Congress with little legislative power and few allies in their party’s caucus, these conservatives believe they have assets more valuable than Washington clout: a shared language with the party’s base, and a political intuition that echoes Mr. Trump’s.

In the months since the former president left the White House, Republican donors and party leaders have flocked to more established figures like Gov. Ron DeSantis of Florida and Senator Tim Scott of South Carolina, stirring buzz for their presidential prospects. At the same time, right-wing Republicans like Ms. Greene and Mr. Gaetz are loudly making the case that the post-Trump version of the Republican Party won’t swing back toward the center but will double down on the former president’s most controversial qualities.

With that in mind, the two Republicans traveled to Iowa with a message about their fellow conservatives. It was not enough, they suggested, to insult Democrats as traitors to America or to cast doubt on the effectiveness of Covid vaccines and the legitimacy of the 2020 election. They told rally attendees that winning back the House in 2022 would be useless without more “America First” Republicans and that beating President Biden would require a full embrace of Mr. Trump.

They sought to up the rhetorical ante on issue after issue, creating new litmus tests for their conservative rivals in the process.

“Last time Republicans had full control, the first year under President Trump, Republicans didn’t fund and build the wall,” Ms. Greene said to the crowd of about 200 people. “Republicans didn’t defund sanctuary cities, they funded them. And this is the one that blows my mind: They did not defund Planned Parenthood.”

She added, “This time around, Republicans need to take back the House with people that are going to do as they say.”

Mr. Gaetz said that unlike many Republicans in Congress, he and Ms. Greene did not take corporate donations, arguing that many in the party were “too often shills for big business.” (Both of them, especially Ms. Greene, have demonstrated small-dollar fund-raising prowess.)

In interviews, Republicans who went to the rally or who have followed Ms. Greene and Mr. Gaetz from afar said the pair’s efforts should not be discounted. In 2016, Mr. Trump stormed through the Republican primary and swept to power after party leaders underestimated the grass-roots appetite for his openly anti-immigrant language, his insults toward G.O.P. leaders and his economic message that targeted some corporations.

Now, Mr. Gaetz and Ms. Greene appear intent on doing the same thing, to set the table for another presidential run by Mr. Trump or to send a warning shot to any would-be successors.

If their bet is correct and the Republican base has left the Trump era wanting more of his bombastic style, it will have profound effects on the country’s political landscape. At minimum, Trump loyalists have shown themselves to be a stubborn force, threatening to pull additional congressional and presidential candidates into the waters of misinformation and racial intolerance.

Kathy Pietraszewski, a 69-year-old rally attendee from Des Moines, said she had formally left the Republican Party after the 2020 election because she believed leaders were insufficiently supportive of Mr. Trump’s attempts to overturn the results. Recently, she has focused on speaking out against Covid vaccines, which is part of the reason she likes Ms. Greene.

“I know what the globalist agenda is, and their one world order starts with a vaccine,” Ms. Pietraszewski said. “So my No. 1 issue is freedom.”

Polling and voter registration data suggest she is not alone. The Republican base, unlike the Democratic one, has a much higher tolerance for politicians who criticize their own party, and many Republicans still want Mr. Trump to be involved in the party’s future, according to a recent Associated Press-NORC poll. Vaccine skepticism and distrust in the 2020 election results are also high among conservative Americans. In May, a Quinnipiac University poll found that two-thirds of Republicans believed Mr. Biden’s victory was not legitimate.

However, both Ms. Greene and Mr. Gaetz face significant hurdles to advancing their political careers.

Mr. Gaetz is the subject of a Justice Department investigation of whether he had a sexual relationship with a 17-year-old and paid for her to travel with him, according to people briefed on the matter. Ms. Greene has set off a series of controversies since she took office early this year, repeatedly using antisemitic and Islamophobic language and endorsing the executions of Democrats.

Ms. Greene has since been stripped of her House committee assignments, but she has found an audience with Mr. Trump and his allies in the conservative media ecosystem. Several attendees at the Iowa rally said they had heard about her appearance there from a podcast run by Steve Bannon, the former Trump adviser.

“We know what American people want,” Ms. Greene said. “We know for a fact what you want. We don’t buy into the swamp.”

In Washington, the two members of Congress are treated like little more than a media sideshow, a nuisance for Republican leaders. They do not have traditional legislative power, and antics like Ms. Greene’s promise to bring impeachment articles against Mr. Biden gain no traction in Congress.

Their words support Mr. Trump’s core policies: cutting immigration, attacking liberal messaging on race and policing, targeting big tech companies. But Brian Robinson, a Republican strategist from Georgia, said there was a big difference between someone who excites activists and someone who has Mr. Trump’s universal name recognition and business-friendly persona.

“A person like Marjorie Taylor Greene attracts crowds and attention because they are speaking to an audience that feels marginalized but also mobilized, because they’re angry,” he said.

“But revving up certain segments of the party can also alienate other parts of the party,” he added, saying the same thing happens to Democrats.

Michael Murphy, a Republican consultant based in California, said, “They fascinate the media,” but added that “as far as real muscle, even in the Republican primary, they’re just one of many factions.”

Still, Ms. Greene and Mr. Gaetz may have the next-best thing, according to rally attendees, other close watchers of the Republican Party and even some liberals. They are messengers of the type of white grievance politics that Mr. Trump deployed nationally. They say openly what others will only hint at, no matter its factual basis or the risk of backlash. And they speak with the fearful moral urgency that many Republican voters feel.

“It’s hard for me to think about 2024, because I don’t know if we’ll make it there,” Ms. Pietraszewski said, expressing dire worries about the country’s future. “With the Black Lives Matter and Marxism and critical race theory, I don’t know.”

At the rally, Ms. Greene called Representative Ilhan Omar of Minnesota, who is Somali-born, “a traitor to America.” Mr. Gaetz said that Defense Secretary Lloyd J. Austin III, the first Black person to serve in that role, “might be the stupidest person to have ever served in a presidential cabinet in America’s history.” Ms. Greene declared that the United States faced a new “axis of evil” made up of the news media, Democrats and big tech companies. They both promised to support the Jan. 6 Capitol rioters who had been arrested.

Each comment drew applause.

“I’m not voting for anyone who won’t say Donald Trump had the election stolen from him,” said Ron James, a 68-year-old retiree from Des Moines. “And I don’t think anyone in that room would, either.”