MARION, Iowa—Jan Landgren likes several Republican presidential candidates, but is now leaning hard toward Texas Sen. Ted Cruz after his father came here and declared: “Did you know that the Bible tells you exactly who to vote for?”

Rafael Cruz, an evangelical pastor who recently spoke to about 200 people at Grace Baptist Church in this Cedar Rapids suburb, recited guidelines for choosing political leaders that he found in Exodus 18:21—select people who are able, God-fearing and truthful, among other virtues.

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