The fundraising text accused donors of being traitors, saying they'd be "branded a deserter" if they didn't contribute.
"Really is incredible how close we came, and how some want to just 'move on,'" the Republican congressman wrote.
"I don't think anybody should be testing our patience at this point," the Democratic congressman warned.
"The Republican Party will not get better unless you stand up," the congressman said in a message to fellow GOP lawmakers on Saturday.
"It is time for the Republican Party to denounce militia-ism," the GOP lawmaker urged.
The Illinois GOP congressman said that there are some Republican lawmakers who "only care about what it means for their votes and their bottom line as politicians."
The GOP House Minority Leader has helped five anti-Trump Republicans raise about $100,000 each in the first half of 2021.
Representative Matt Gaetz questioned how Republicans are supposed to "trust" the GOP House leader in a Thursday tweet.
"I wonder what @GOPLeader [Kevin McCarthy] thinks of this statement?" the Illinois Republican asked.
"My party has to embrace truth," the Illinois Republican said. "We have to have a full reckoning of what happened on January 6."
The GOP congressman's criticism comes as Republicans continue to push for probes of last year's presidential election—10 months after it was held.
The Republican congressman admitted last weekend that he spoke with Trump "more than once" during the Capitol attack.
The House Freedom Caucus has urged GOP Leader Kevin McCarthy to oust Cheney and Kinzinger from the House Republican Conference.
"The enemy gets a vote too," the Republican congressman tweeted.
During an appearance on CNN Sunday, the Illinois Republican congressman said both parties are responsible for the situation in Afghanistan.
"Are we going to be the party that keeps stoking sympathy for domestic terrorists and pushes out truth, or finally take a stand for truth," Kinzinger tweeted.
The Republican congressman has raised concerns over the situation in Afghanistan, criticizing the current and the former administrations.
The former congressman said the U.S. "could spend additional billions of dollars and lose even more lives, but it would only forestall this outcome and leave us no safer."
"The Trump/Biden calamity unfolding in Afghanistan began with the Trump administration negotiating with terrorists," Cheney said Saturday.
"From the start, the mission was flawed by design," Senator Chris Murphy, a Democrat, said of the Afghanistan War.
"If anybody's scared of this investigation I ask you one question, what are you afraid of?" the GOP lawmaker said.
Representative Lauren Boebert said Liz Cheney and Adam Kinzinger "have done more to hurt" Republicans than help.
Kinzinger choked up as he addressed officers during the first hearing of the House select committee investigating the January 6 riot at the U.S. Capitol.
"We must know what happened here at the Capitol. We must also know what happened every minute of that day in the White House," Liz Cheney said at the hearing.
Law enforcement officers who testified at the hearing described rioters beating them with "any items they could get their hands on," such as flagpoles, tasers and rocks.
She said Sunday that Kinzinger "brings great patriotism to the Committee's mission: to find the facts and protect our Democracy."
"You either have to be a zombie for the MAGA belief system...or actually stand up and tell your constituents the truth," Kinzinger said Sunday.
"The Taliban always had a saying: 'America has the watches but we have the time,'" said the congressman.
GOP Rep. Madison Cawthorn suggested the outreach program, or the mechanism behind it, could eventually be used to "take your guns, take your Bibles."
"It's confusing because I thought so many of the people I know, like Kevin McCarthy, had a red line that they just wouldn't cross, that there would be no payoff worth crossing that line," Kinzinger said.