Eleven members of his family signed a letter lambasting him for his vote last month to impeach the then-president, who they defended as a Christian.
“Oh my, what a disappointment you are to us and to God!” they wrote, accusing Kinzinger of going “against your Christian principles” and joining the “devil’s army.”
"It is now most embarrassing to us that we are related to you," they added.
His relatives also sent the letter to other conservative lawmakers.
“We should listen even more grievances against you, but decided you are not worth more of our time to list them,” the letter from his relatives continued. “You have embarrassed the Kinzinger family name!”
Kinzinger, one of 10 House Republicans who voted to impeach Trump last month, also voted this month to strip Rep. Majorie Taylor Greene, R-Ga., of her committee posts for espousing conspiracy theories.
He’s betting his career on disavowing Trumpism, pushing for an alternative path for the GOP. He recently launched a "Country 1st" political action committee, which seeks to put some money behind the political effort confronting a party largely still aligned with the former president.
"The reality is this — this is the time to choose," Kinzinger said during an interview with NBC's "Meet the Press" on Jan. 31. "Let's take a look at the last four years how far we have come in a bad way, how backward-looking we are, how much we peddle darkness and division. That's not the party I ever signed up for."
In the interview, he hinted at the letter, saying he'd received two certified letters "disowning me."
It's likely to be an uphill, lonely battle: During the impeachment vote, Kinzinger asked Democrats for more speaking time to make a bipartisan pitch for the impeachment of Trump, according to the Times, but was denied. Republican Rep. Liz Cheney of Wyoming voted to impeach Trump and only narrowly held on to her leadership position in the House when her party mounted an effort to strip her of it.