Former Rep. Joe Walsh (R-Ill.), the conservative talk-show host and prominent “tea party” figure, on Wednesday called President Donald Trump an “unfit conman” and a “racial arsonist” and urged a primary challenge for the Republican nomination next year.

Walsh also apologized both for his own heated rhetoric over the years and for helping to elect Trump in 2016.

Writing in The New York Times, Walsh said:

“In Mr. Trump, I see the worst and ugliest iteration of views I expressed for the better part of a decade. To be sure, I’ve had my share of controversy. On more than one occasion, I questioned Mr. Obama’s truthfulness about his religion. At times, I expressed hate for my political opponents. We now see where this can lead. There’s no place in our politics for personal attacks like that, and I regret making them.”

Walsh voted for Trump in 2016.

“If Trump loses, I’m grabbing my musket,” he wrote on Twitter, later saying it wasn’t a literal call to arms but a call to protest.

However, since the election, he’s turned into a persistent Trump critic from the right.

In the Times, he argued that Trump isn’t a conservative and that he’s vulnerable not just because he’s unfit for office but because of his poor record.

“He’s reckless on fiscal issues; he’s incompetent on the border; he’s clueless on trade; he misunderstands executive power; and he subverts the rule of law,” Walsh wrote. “It’s his poor record that makes him most worthy of a primary challenge.”

He noted that former Massachusetts Gov. William Weld, who is running against Trump in the Republican primary, is a centrist challenger. Instead, Walsh said, Trump could be vulnerable to a conservative opponent in the primary:

“We need someone who could stand up, look the president in the eye and say: ‘Enough, sir. We’ve had enough of your indecency. We’ve had enough of your lies, your bullying, your cruelty, enough of your insults, your daily drama, your incitement, enough of the danger you place this country in every single day. We don’t want any of this anymore, and the country certainly can’t stand four more years of it.’”

Read the full column here.

On Twitter, Walsh wrote that his column was both a call for someone to run against Trump and an apology for his own role in helping to elect him: