In the weeks following the attack on the Capitol, many Americans have argued over whether the violence was a singular event or an outcome of deeper forces. Voters, Congress and a former president are clashing over who is to blame.

To Kelly J. Baker, a writer and public scholar of religion and racial hatred, the attack felt familiar, and it made her nervous. Many rioters, a largely white group, were motivated by religious fervor and saw themselves as participants in a kind of holy war. Some brought Confederate flags, others crosses. Some who invoked the name of Jesus were members of far-right groups like the Proud Boys, whose participants have espoused misogynistic and anti-immigrant views. Some were motivated by conspiracy theories and QAnon falsehoods as well as their conservative Christian faith.

In many ways it resembled the culture of the Ku Klux Klan in the 1920s, and the group’s march on Washington in 1925, said Dr. Baker, who previously was a religious studies lecturer at the University of Tennessee. Many Americans associate the K.K.K. with white hoods, burning crosses and anti-Black racism but are less familiar with its white Protestant ambitions and antipathy toward Catholics and Jews. Dr. Baker explores that history in her book “Gospel According to the Klan: The KKK’s Appeal to Protestant America, 1915-1930,” published by the University Press of Kansas in 2011.

In a conversation with The New York Times that has been edited for length, Dr. Baker reflected on how white Protestant Christianity and nationalism have long been interwoven — even a mainstream movement — and how many white churches today have yet to reckon with white supremacy.

I thought I’d start with a blunt question. Are connections between white Christianity and extremism new?

No. White Christianity and this white supremacist Trump extremism are definitely not a new combination. I’d push back a little bit about the language of extremism to say that some of this stuff has been remarkably mainstream in American history. I just think that what we’re seeing right now is a dramatic form of it.

What did the attack on the Capitol remind you of historically?

It reminds me of some of the actions of the 1920s Klan, where they are marching on Washington in hoods and robes and carrying flags and crosses to show their dominance and presence in American life.

This was the largest order of the Klan in American history, millions of members in all 48 continental states. Usually the estimates are four to six million. Folks were bankers and dentists and lawyers, pastors and politicians. This involved both white men and women. They stood for, explicitly, white supremacy and white Protestantism. Arguably, it is an evangelical movement too. For membership you were supposed to be a white Christian. You had to be supportive of nationalism and patriotism. They actively encouraged members to go to church. Their language was definitely influenced by evangelicalism, the way they talk about Jesus Christ as their Lord and Savior.