Walsh stands virtually no chance of wresting the Republican presidential nomination from Trump, whose approval rating with Republican voters is consistently in the high 80s, and whose political aides have been aggressively moving to tighten their control over state parties to thwart primary challenges.

But those encouraging Walsh, a Tea Party conservative who served one term in the House and went from staunch Trump supporter to acerbic critic, hope he can appeal to reluctant Trump voters who are open to an alternative.

In 2016, Walsh wrote on Twitter that he was voting for Trump, adding: “On November 9th, if Trump loses, I’m grabbing my musket. You in?” Now, Walsh is calling the president a “racial arsonist” and hoping to turn his fighter personality around on Trump to help defeat him.

Before his likely announcement, according to two people who have spoken with him, Walsh has hired a senior political adviser, organized meetings with high-profile Trump antagonists in New York City, and published an op-ed in The New York Times with the goal of previewing his campaign message.

Walsh has yet to definitively say whether he is running. “If I do it, it’s going to be before Labor Day,” he said in an interview.

Once an ardent and vocal critic of Hillary Clinton, Walsh said the breaking point for him came last year during Trump’s meeting in Helsinki with President Vladimir Putin of Russia.

“He lost me for good in Helsinki, when he stood in front of the world and said, ‘I believe Putin and I don’t believe my fellow Americans,’” Walsh said, framing a potential run as a moral imperative “to stick our necks out because when people see that, more and more people will.”

Walsh is being encouraged by William Kristol, the conservative writer and former editor of the now-defunct magazine The Weekly Standard. Kristol has been a “Never Trump” Republican since Trump was elected in 2016 and has been working hard over the past year to recruit someone to run against him.

Kristol said Walsh’s comfort with the in-your-face format of conservative talk radio makes him a potentially more effective combatant against Trump than someone like William Weld, the genteel former governor of Massachusetts, whose own primary challenge to the president has gained little traction.

“He has a different appeal than Bill Weld,” Kristol said. “The fact that he was a Tea Party congressman who voted for Trump in 2016 gives him an ability to speak to Republican primary voters that ‘Never Trumpers’ like me don’t have.”

Tim Murtaugh, a spokesman for Trump’s campaign, responded to a request for comment with two words about Walsh’s possible challenge: “Certain failure.”

But Lucy Caldwell, an adviser to Walsh, said she planned to make an appeal to “traditional campaign consultants who should look beyond fear of losing an RNC contract, and think about why they got into politics in the first place.”

Trump’s advisers have been mindful for over a year that primary challenges can expose weaknesses in reelection efforts, and can conclude with messy delegate fights on the floor of the Republican National Convention. Led by Bill Stepien, a former White House political director, they have been working to tighten their stranglehold on state parties to make it virtually impossible for any primary challenger to amass delegates.

Some Trump advisers are more concerned about a primary challenge than they publicly let on, as Trump faces more strain in the job than he has in many months. They are also aware that primary challenges can weaken incumbents in a general election. The most recent example was President George H.W. Bush, who faced a primary challenger from the right in 1992 from Patrick Buchanan, a former aide to Richard Nixon and a prominent conservative.

In Trump’s case, there is little to no space to his right for a challenger to occupy. And his lock on Republican voters has remained solid. But primaries can drain energy and resources, particularly when the president is increasingly focusing on distractions, like a feud with his 11-day communications director, Anthony Scaramucci, who has recently turned against his former boss, calling him a “demagogue” and encouraging Republicans to take a stand against him.

Some public polling has found that more than 40% of Republicans are open to a primary challenge to Trump.

“One of the things that is clear is that there is a high interest in an alternative,” said Sarah Longwell, a Republican strategist who has been working with Kristol on a group called Defending Democracy Together, to resist Trump from within the party.

“People say they like the economy and some of the things he’s doing on immigration and judges, but he’s divisive and doesn’t tell the truth,” Longwell added. “People have eyes. They’re very clear about who this person is. These are not the people who attend the rallies.”

Kristol, who acknowledged that he had made several efforts at recruiting a Republican to take on Trump, admitted that the race would be “David and Goliath,” with Walsh as the underdog.

“But I think he’s a good David,” he said.

In his New York Times op-ed, Walsh said he regretted some of the excesses of his own political career like questioning President Barack Obama’s “truthfulness about his religion” and expressing “hate for my political opponents,” noting “we now see where this can lead.”

He called Trump “unfit for office” and wrote that “in Mr. Trump, I see the worst and ugliest iteration of views I expressed for the better part of a decade.”

Walsh said he was aware of the challenges that he would face if he ran. Among them will be the almost certainty of losing his radio show.

“Unless you wash this guy’s feet every day,” he said, “it’s hard to keep a radio show or TV show in conservative media.”

This article originally appeared in The New York Times.