Senator JD Vance of Ohio will campaign Saturday in Pennsylvania with Lance Wallnau, a self-described prophet who has said that former President Donald J. Trump was chosen by God, defended the Jan. 6 attack on the Capitol and described Vice President Kamala Harris’s debate performance as “witchcraft.”

Mr. Wallnau, an evangelical influencer from Dallas, has become a big name in the charismatic movement of Christianity. A corporate marketer who became a celebrity prophet, he applies his marketing skills to push prosperity gospel teachings and products. He is especially well known for the belief that Christians should influence or even rule society, from politics to media to culture to the economy.

In a recent online conversation about Ms. Harris’s performance at the debate earlier this month, Mr. Wallnau said that she could “look presidential.”

“That’s the seduction of what I would say is witchcraft,” he said. “That’s the manipulation of imagery that creates an impression contrary to the truth, but it seduces you into seeing it. So that spirit, that occult spirit, I believe is operating on her and through her, similar to with Obama.”

Mr. Wallnau has defended the Jan. 6, 2021, attack on the Capitol by pro-Trump rioters, downplaying the violence or justifying it as righteous. He recently told a crowd of supporters in Eau Claire, Wis., that “Jan. 6 was not an insurrection, it was an election fraud intervention,” according to CBS News.

A spokeswoman for the Democratic National Committee, Aida Ross, criticized Mr. Vance for appearing with Mr. Wallnau, whom she called “a conspiracy theorist whose record includes accusing women of ‘witchcraft.’”

“This shameless pandering to the far-right is exactly what the American people have come to expect from Vance,” she said in a statement, “and it’s why he’s the least popular VP nominee in modern American history whose disastrous reputation will be yet another drag on the Trump-Vance ticket this November.”

Mr. Wallnau was one of Mr. Trump’s earliest evangelical supporters in 2015 and has been traveling through battleground states seeking to mobilize Christian voters. He has praised Mr. Trump as a modern King Cyrus, who was the ancient emperor of Persia lauded in the Bible for freeing God’s people from captivity in Babylon.

Evangelical support of Mr. Trump remains strong. Mr. Wallnau’s event with Mr. Vance illustrates how what was once a fringe movement at the edge of Republican politics has pushed into the mainstream.