Stephen K. Bannon, White House chief strategist, is viewed warily by some old-line Republicans. (Matt McClain/The Washington Post)

When House Speaker Paul D. Ryan’s redbrick Georgian revival house in Janesville, Wis., was surrounded last July by women whose children were murdered by undocumented immigrants, conservative writer Julia Hahn published a scathing report and a blurry snapshot of Ryan’s departing SUV.

The headline: “Paul Ryan flees grieving moms trying to show him photos of their children killed by his open borders agenda.”

Three months later, Hahn wrote a 2,800-word story alleging that Ryan (R-Wis.) was the ringmaster for a “months-long campaign to elect Hillary Clinton.” It was just one of a torrent of posts over the past year that cast Ryan as a “globalist” who is cozy with corporations and an enemy of Donald Trump-style populism.

Now Hahn, 25, is expected to join the White House staff, serving as an aide to strategist Stephen K. Bannon, the controversial former Breitbart chairman and a powerful confidant of President Trump.

“She’ll be Bannon’s Bannon and make Bannon look moderate,” said William Kristol, the editor at large of the Weekly Standard, a conservative magazine. “Her tendency is to fight and fight, often to the extreme.”

(Jenny Starrs/The Washington Post)

Although Hahn will serve in a midlevel role as a special assistant to the president, her hiring alarmed and angered several Ryan allies, who expressed concern Monday about what they see as a brazen move by Bannon that threatened the fragile comity between Trump and Congress — and brightly underscored the Trump team’s insouciance about enlisting Ryan’s fiercest critic.

Privately, a number of House Republicans told The Washington Post that Hahn’s involvement signaled Bannon’s plans to possibly put her to use against them, writing searing commentaries about elected Republican leaders to ram through Trump’s legislative priorities and agitate the party’s base if necessary.

“This is obviously a provocative act and clearly an intentional act,” said Peter Wehner, a longtime Ryan friend and former official in three Republican administrations. “Bannon is willing to napalm the bridges with congressional Republicans.”

Wehner said that too many Republicans on Capitol Hill are “engaging in a fiction, a game, where Bannon and Trump aren’t taken seriously even though Bannon and Trump are operating in a serious way and bringing on people who are going to work for their cause, not for conservatives.”

Stuart Stevens, who served as chief strategist for the Romney-Ryan 2012 presidential campaign, said that “Bannon has been at war with the Republican Party, and that hasn’t changed” with Hahn’s hire.

“In the Bannon-Ryan split, I’m on the Ryan side,” Stevens said. “I don’t consider what he’s doing to be populism, either.”

Other Ryan associates were less perturbed and pointed out that Bannon was among the Trump advisers who had an agreeable meeting at the Capitol this month to coordinate their plans for tax reform.

“Let’s wait and see what she and Bannon end up doing,” said Bob Woodson, a veteran community organizer who is close to Ryan. “Bannon’s been there, and it hasn’t fallen apart. Everyone is trying to figure the whole thing out.”

Said William J. Bennett, a mentor to Ryan for decades: “My sense is that Trump has a good feeling these days toward Ryan and that the feeling is mutual. I’m hopeful those feelings will continue.”

Ryan spokesman Brendan Buck dismissed the suggestion of any tensions because of Hahn coming to the White House. “We could not care less,” he said in a statement.

The White House did not respond to a request for comment about Hahn, whose position has not been announced.

Politico first reported Hahn’s hiring.

Trump welcomed Ryan and other congressional leaders to the White House on Monday and is preparing to meet with congressional Republicans later this week in Philadelphia at a GOP retreat. Trump advisers are working with Ryan’s team to map out the president’s proposals on a slew of issues, including health care, taxes and infrastructure projects.

Hahn’s hiring is the latest pull in an ongoing and informal tug-of-war over the direction of Trump’s presidency and the political tint of the people working from the small offices in and around the Oval Office.

“As far as I can tell, she is only the third or fourth member of the Trump administration who actually supports Trump on his main issues — immigration, trade and no more war,” said Ann Coulter, a conservative author and Trump supporter.

Hahn joins a staff that includes Bannon and Stephen Miller, a populist firebrand and policy guru. Even as Trump aides work together, there are internal debates over how populist the president should be and how much he should strike traditionally Republican notes. Bannon and Miller, along with Sen. Jeff Sessions (R-Ala.), Trump’s nominee for attorney general, are widely seen as the “populist-nationalist wing” of Trump’s administration, while Chief of Staff Reince Priebus and Vice President Pence are frequently described as the more mainstream Republican players.

Trump, who has a loose approach to management and seeks counsel from a sprawling network, has been veering between these two main blocs on his staff as he begins his presidency.

During an interview last week with The Post, Trump affectionately referred to Miller and Bannon as “my two Steves.”

“I’m here with my two Steves,” Trump began. “We’re having a very important meeting, so give me a few minutes.”

Bannon, meanwhile, has been bolstering his own profile internally since the election, working alongside Trump’s son-in-law and senior adviser Jared Kushner — a former publisher of the New York Observer — to craft policy and build the Cabinet, according to people familiar with their discussions. Priebus has worked in coordination with them, but Bannon and Kushner have developed a deeper bond as former media executives and digital-savvy operatives, the people said. They were not authorized to speak publicly.

Hahn studied philosophy at the University of Chicago and was a producer for Laura Ingraham’s ­radio program and press secretary for the anti-establishment Rep. David Brat (R-Va.), who toppled House Majority Leader Eric Cantor in the 2014 primary. She remains mostly unknown outside of Washington and avoids television appearances and shuns social media. Her colleagues refer to her as a “ghost” because she is not on Twitter.

But among many House Republicans and those close to Ryan, Hahn has become an infamous figure whose blizzard of razor-edged stories about supposed GOP inaction on stopping illegal immigration and curbing Muslim immigration to the United States has caused them headaches with activists.

One notable clash came at a gathering of conservative House lawmakers in 2015. Hahn pressed the members at a news conference about whether they would support “a suspension or reduction in Muslim immigration.”

“I don’t answer questions from you because you are not a truthful reporter, and I will not answer any of your questions,” Rep. Raúl R. Labrador (R-Idaho) said. “So let’s move on to somebody else.”

Despite her close ties to Bannon and the roiling, Trump-embracing quarters of the American right, Hahn has not always supported Trump’s decisions. She has assailed his nominee for secretary of labor, Andrew Puzder, as someone who “prefers foreign labor to American workers.”

Speaking on Breitbart radio last month, Hahn said Trump should instead populate the administration with people are willing to be “twisting arms” in support of hard-line trade and immigration policies.

She was hired a few weeks later.