Adam Kinzinger represented a reliably Republican district in the US House for six terms. He voted to impeach Donald Trump over the insurrection and with Liz Cheney was one of two Republicans on the January 6 committee. Like the former Wyoming congresswoman, he earned the ire of Trump and the GOP base.

A lieutenant colonel and air force pilot, Kinzinger read the terrain and declined to run again. In his memoir, he looks back at his life, family and time in the US military. He also examines the transformation of the Republican party into a Trumpian vessel. With the assistance of Michael D’Antonio, biographer of Mike Pence, he delivers a steady and well-crafted read.

Kinzinger finds the Republicans sliding toward authoritarianism, alienating him from a world he once knew. On 8 January 2021, two days after the Trump-inspired coup attempt, he received a letter signed by 11 members of his family, excoriating him for calling for the president to be removed.

“Oh my, what a disappointment you are to us and to God!’ the letter began. “We were once proud of your accomplishments! Instead, you go against your Christian principles and join ‘the Devil’s army’ (Democrats and the fake news media).”

The word “disappointment was underlined three times”, Kinzinger counts. “God once.”

Elected in 2010 with the backing of the Tea Party, once in office, Kinzinger distanced himself from the Republican fringe. The movement felt frenzied. Hyper-caffeinated. He cast his lot with Eric Cantor, House majority leader and congressman from Virginia. “Overtly ambitious”, in Kinzinger’s view, Cantor also presented himself as “serious, sober and cerebral”. Eventually, Cantor found himself out of step with the enraged core of the party. In 2014, he was defeated in a primary.

Cantor was too swampy for modern Republican tastes. Out of office, he is a senior executive at an investment bank.

Simply opposing Barack Obama and the Affordable Care Act wasn’t enough. With America’s first Black president in the White House, performative politics and conspiracy theories took over.

Kevin McCarthy, deposed as speaker last month, earns Kinzinger’s scorn – and rightly.

“I was not surprised he was ousted,” Kinzinger told NPR. “And frankly, I think it couldn’t happen to a nicer guy.”

On the page, Kinzinger paints McCarthy as weak, limitlessly self-abasing and a bully. He put himself at the mercy of Matt Gaetz, the Florida extremist, prostrated himself before Marjorie Taylor Greene, the Georgia extremist, and endured 15 rounds of balloting on the House floor to be allowed the speaker’s gavel – an illusion of a win.

McCarthy behaved like “an attention-seeking high school senior who readily picked on anyone who didn’t fall in line”, Kinzinger writes. The California congressman even tried, if feebly, to physically intimidate his fellow Republican.

“Once, I was standing in the aisle that runs from the floor to the back of the [House] chamber,” Kinzinger remembers. “As [McCarthy] passed, with his security man and some of his boys, he veered towards me, hit me with his shoulder and then kept going.”

Apparently, McCarthy forgot Kinzinger did stints in war zones.

Kinzinger also takes McCarthy to task for his shabby treatment of Cheney, at the time the No 3 House Republican. On 1 January 2021, on a caucus call, she warned that 6 January would be a “dark day” if they “indulged in the fantasy” that they could overturn Joe Biden’s victory over Donald Trump.

McCarthy was having none of it. “I just want to be clear: Liz doesn’t speak for the conference,” he said. “She speaks for herself.”

That, Kinzinger writes, was “unnecessary and disrespectful, and it infuriated me”.

These days, McCarthy faces the prospect of a Trump-fueled primary challenge. But he is not alone in evoking Kinzinger’s anger. Kinzinger also has tart words for Mitch McConnell and his performance post-January 6. The Senate minority leader was more intent on retaining power than dealing with the havoc wrought by Trump and his minions, despite repeatedly sniping at him.

When crunch time came, McConnell followed the pack. Kinzinger bemoans McConnell’s vote to acquit in the impeachment trial, ostensibly because Trump had left office, and then his decision to castigate Trump on the Senate floor when it no longer mattered.

“It took a lot of cheek, nerve, chutzpah, gall and, dare I say it, balls for McConnell to talk this way,” Kinzinger bristles, “since he personally blocked the consideration of the case until Trump departed.”

Kinzinger devotes considerable space to his own faith. An evangelical Protestant, he is highly critical of Christian nationalism as theology and as a driving force in the Republican party. He draws a direct line between religion and January 6. Proximity between the cross, a makeshift gallows and calls for Mike Pence to be hanged was not happenstance.

“Had there not been some of these errant prophecies, this idea that God has ordained it to be Trump, I’m not sure January 6 would have happened like it did,” Kinzinger said last year. “You have people today that, literally, I think in their heart – they may not say it – but they equate Donald Trump with the person of Jesus Christ.”

In his book, Kinzinger echoes Russell Moore, former head of public policy of the Southern Baptist Convention: “Moore’s view of Christianity was consistent with traditional theology, which does not have a place for religious nationalism. Nothing in the Bible said the world would be won over by American Christianity.”

Looking at 2024, Kinzinger casts the election as “a simple question of democracy or no democracy … if it was Joe Biden and Donald Trump, I don’t think there’s any question I would vote for Joe Biden”.

• Renegade is published in the US by Penguin Random House