Former Pennsylvania Sen. Rick Santorum vowed Friday to pursue immigration policies that protect American workers, while warning voters that some of his GOP rivals have embraced a much softer approach to the issue. Mr. Santorum, the runner-up in the 2012 Republican nomination battle, urged the crowd that converged on a hotel in Washington, D.C., for the annual Values Voter Summit to recognize that a couple of the speakers before him — Sens. Marco Rubio and Ted Cruz — have previously supported “amnesty” for illegal immigrants. “You have a lot of people that come up here and talk about how tough...