The Republican congressman Adam Kinzinger said on Sunday he would fight the “cancer” of Trumpism outside the congressional GOP, after he retires from the House next year.

“In the House you can fight to try to tell the truth,” the Illinois representative said, speaking to ABC’s This Week. “You can fight against the cancer in the Republican party of lies, of conspiracy, of dishonesty.

“And you ultimately come to the realisation that basically it’d be Liz Cheney and a few others that are telling the truth and there are about 190 people in the Republican party that aren’t going to say a word, and there’s a leader of the Republican caucus [Kevin McCarthy, the House minority leader] that is embracing Donald Trump with all he can.”

Asked if he had handed Trump a “win” by quitting, he said he “potentially” had but added: “It’s not really handing a win as much to Donald Trump as it is to the cancerous kind of lie and conspiracy, not just wing anymore, but mainstream argument of the Republican party.”

Kinzinger and Cheney were among 10 House Republicans who voted to impeach Trump for inciting supporters to attack the Capitol on 6 January, in an attempt to overturn the election.

That made Trump’s second impeachment the most bipartisan ever. Seven Republican senators voted to convict, not enough for a required super-majority, ensuring Trump’s acquittal.

Another House Republican who voted for impeachment, Anthony Gonzalez of Ohio, has announced his retirement. Trump greeted Kinzinger’s announcement by saying: “Two down, eight to go.” Others including Cheney have attracted challengers.

Kinzinger and Cheney are the only Republican members of the House select committee investigating 6 January. McCarthy withdrew co-operation when the speaker, Nancy Pelosi, rejected an attempt to put Trump allies on the panel.

Kinzinger told ABC Trump’s lawsuit to stop the committee accessing presidential records held in the National Archives was an attempt to drag proceedings out long enough for Republicans to retake the House next year and thereby kill the investigation.

“Look, they killed an independent commission,” he said. “They’ve killed any attempt to get to the truth. [But] we have sources beyond just those that are kind of making the news, the Steve Bannons, you know, the Archives. We have people coming in and talking to the committee every day.

“I think if you look at that archive request and what the former president is trying to block, it is very telling when you look at things like call logs, etc … We are going to fight as hard as we can to get that, and the president has no grounds to claim executive privilege as he is today.”

Trump supporters, dominant in a GOP fully under the former president’s control, greeted Kinzinger’s retirement announcement with glee and abuse – despite the fact that as a strong conservative, he mostly voted with Trump during Trump’s time in office.

Kinzinger told ABC he intended to stay in politics.

“The point is there’s a lot of people that feel politically homeless, there’s a lot of people that feel like something has to change in our politics, and I think it’s important to jump in with both feet and see where that goes. See if there’s that market out there because what’s happening, we’re failing the American people right now.

“The political system is failing. And the Republicans in particular.”

Kinzinger admitted that redistricting by Illinois Democrats that would affect his chances of re-election was part of his decision, saying: “I’m not complaining, it’s redistricting, I get it, it’s being done and abused everywhere. But when Democrats do say they want Republican partners to tell the truth, and then they specifically target me, it makes me wonder.”

But he said a stronger push to retire had come from the direction of his party under Trump.

“It’s sitting back and saying, ‘OK, what happens if I win again? I go back, probably Republicans will probably be in the majority. I’m going to be fighting even harder … and I haven’t seen any momentum in the party to move away from lies and towards truth.”