What is Christian nationalism? Unless you're a devoted student of religion and politics, you'd be forgiven for wondering. The concept has circulated for decades in scholarly circles, where it was more often used in an international context than applied to the United States. But since 2016, it's become a popular term of art for Christian conservative politics. Georgetown international affairs professor Paul D. Miller defines Christian nationalism as "the belief that the American nation is defined by Christianity, and that the government should take active steps to keep it that way." Sociologists Andrew Whitehead and Samuel Perry use six criteria, including belief that the federal government should declare the U.S. a Christian nation and that American success is "part of God's plan."