Adam Kinzinger has set up a new political action committee to fight back against the right wing of his own party.
The Air Force veteran said that he was driven to launch the “Country First” PAC after violent pro-Trump rioters at the capitol tried to prevent Joe Biden’s victory being certified.
“This is no time for silence. Not after the last month. Not after the last few years. Someone needs to tell the truth,” he said in a video announcing the campaign.
The attack on the Capitol left five people dead, including a police officer, and led to Mr Trump being impeached for a historic second time for inciting it.
Ten Republicans, including the Illinois lawmaker, joined all 222 House Democrats in impeaching Mr Trump, with 197 Republicans voting against the measure.
QAnon-supporting congresswoman Ms Greene has sparked a string of controversies in her first month in the House of Representatives and supported attempts to keep Donald Trump in power despite his election defeat.
She attempted to impeach Joe Biden the day after his inauguration as president, and her social media history has revealed she seemingly supported executing senior Democrats.
She was also caught on video harassing David Hogg, a survivor of the Parkland school shooting that killed 17 people.
And Ms Greene announced on Saturday that she had had a “great” phone call with Mr Trump amid calls for her to be expelled from Congress.
"The Republican Party has lost its way. If we are to lead again, we need to muster the courage to remember who we are,” said Mr Kinzinger.
“We need to remember what we believe and why we believe it. Looking in the mirror can be hard, but the time has come to choose what kind of party we will be and what kind of future we'll fight to bring about.”
Mr Kinzinger, who served two tours of duty in Iraq, was first elected to Congress in 2010.
"Today's Republican Party is not the one I joined,” he added.
"The party that always spoke about a brighter tomorrow no longer does. It talks about a dark future instead.
“Hope has given way to fear. Outrage has replaced opportunity. And worst of all, our deep convictions are ignored.
“They've been replaced by poisonous conspiracies and lies.
“This is not the Republican road and now we know exactly where new and dangerous road leads. It leads to insurrection and an armed attack on the Capitol.”
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