For generations, American politics has been defined by the outsize influence of Christian conservatives, so much so that the intersection of religion and politics is often treated as the sole province of white evangelicals. And for generations, promises of a rising “religious left” have come and gone without any lasting political imprint. But to look at America’s religious left at this moment is to see something genuinely different. Places of worship are participating in demonstrations for civil rights larger than any protest movement in American history. Democrats like the Rev. Raphael Warnock and Joe Biden—political leaders whose faith isn’t just...