I agree that a religious person would be handy to have in our corner. But I'm not super comfortable with the idea that political questions around religion need a Christian's opinion in order to have impact. It favors political expediency over principles. By doing that, you're slightly conceding that principles aren't important. At the same time, it devalues non-Christian voices on a topic that is most relevant to non-Christians. If Christians only care about the opinions of other Christians, I'm really not trying to play by their rules to win them over.

To be clear, I don't think you're trying to do all that. I also would bet most Christians would agree with this atheist. The minority of actual Christian nationalists aren't going to be convinced no matter what you do. I think a Christian coming out in support of this congressman would be a good show of solidarity across a religious divide. But I don't think this man's argument would be better coming from a Christian instead. It would be like hearing MLK's "I have a dream" speech and saying it would make more sense coming from a white guy because the majority won't listen to him otherwise.