The Lincoln Project said Liz Cheney's election loss marked "the end of the Republican Party."
The anti-Trump group said the party now only bears the GOP "name and branding."
The group called the new GOP "an authoritarian nationalist cult dedicated only to Donald Trump."
The Lincoln Project - an anti-Trump conservative group - said this week that Rep. Liz Cheney's loss in her Wyoming GOP primary race marked the demise of the old Republican Party.
"Tonight, the nation marks the end of the Republican Party," read the organization's statement released Tuesday.
"What remains shares the name and branding of the traditional GOP, but is in fact an authoritarian nationalist cult dedicated only to Donald Trump," the statement added.
Lauding Cheney, the Lincoln Project's team said she had "stood up to the lawless, reckless attack on our nation" that Trump led.
The group also hit out at the Trump-backed Harriet Hageman - who ousted Cheney - calling her a "reality-denying conspiracy theorist who promotes the "Big Lie" and bends a knee to Donald Trump."
"Liz Cheney showed America what a dedicated public servant driven by principle is like; it's no wonder today's GOP hates her," the statement read. "We thank her for her service, and look forward to seeing her next chapter. America needs her and more people like her."
Representatives for Hageman and Trump did not immediately respond to requests for comment from Insider. Insider has also reached out to a representative for the GOP for comment.
Cheney's loss this week marked Trump's biggest primary victory yet. The former president also gloated about her defeat, saying Cheney "can finally disappear into the depths of political oblivion."
Lawyer George Conway - the husband of Trump confidante Kellyanne Conway - was among several Republicans who helped found the Lincoln Project, a political action committee dedicated to keeping Trump from being re-elected.
The organization's leadership warned in 2021 that Trump was a "clear and present danger" and has organized demonstrations to push anti-Trump messages. Its current slate of board members includes political strategists Rick Wilson and Reed Galen.