The night before Shane Claiborne came to town to preach at a Christian revival, he received a letter from the chief of police at Liberty University warning that if he set foot on the property, he would be arrested for trespassing and face up to 12 months in jail and a $2,500 fine.

At first glance, Mr. Claiborne hardly appeared a threat to Liberty University, a dominant force in Lynchburg, Va., and a powerful engine in evangelical Christianity. Wearing baggy clothes that he sews himself, Mr. Claiborne preaches the gospel, lives among the poor and befriends prisoners on death row, modeling his ministry on the life of Jesus.

But to the leaders of Liberty, he was a menace to their campus. He and his national network of liberal evangelicals, called the Red Letter Christians, were holding a revival meeting to protest in Liberty’s backyard. Their target: Jerry Falwell Jr., Liberty’s president and a man who has played a pivotal role in forging the alliance between white evangelicals and Donald J. Trump, who won 81 percent of their vote.