Mr. King, 67, represents the most conservative corner of Iowa, and has long held policy positions rooted in deeply conservative beliefs, especially concerning immigration, which he once deemed a “slow-motion Holocaust.”He has often said he was made aware of illegal immigration as a small child by his father, the one-time mayor of a small Iowa town who taught him to take a hard line. Mr. King dropped out of Northwest Missouri State University to run a construction contracting business, and ran for the State Senate in 1996 when he first cottoned to the idea of an English-only America, something he would push for legislatively throughout his career.“Our language is getting subdivided by some forces of the federal government,” Mr. King once said. “It is time to speak with a common voice. The argument that diversity is our strength has really never been backed up by logic.”He has argued vociferously, long before Mr. Trump ran for office pushing strict anti-immigration measures, including against protections for young adults brought over as children who have been successful in America, a group many Republicans support. In 2006, he suggested a complex plan for building an electrified wall at the border, noting that this was a practice used to control livestock. In 2012, he compared immigrants to dogs.