Sen. John McCain of Arizona has been called many things during his lengthy political career: maverick, straight-talker, the White Tornado. But "border hawk" isn't one of them. Until now. Facing the toughest primary challenge of his 24-year Senate tenure, Mr. McCain has shelved his advocacy of a pathway to citizenship, denounced by its critics as amnesty, and embraced a crackdown on border security that includes the state's new immigration law. The law allows police to question people who they suspect are not citizens and requires them to carry proof of their status. Mr. McCain announced his support for the legislation...