Sen. Marco Rubio sought to blunt a wave of criticism from the conservative Heritage Foundation Thursday with a letter touting the economic benefits of immigration. On Monday, the Florida Republican met with David Addington, group vice president of research at Heritage, and just days later the think tank >slammed the senator’s immigration proposal as a costly “amnesty” program. In a letter to Mr. Addington Thursday, Mr. Rubio said immigration would ultimately be a boon to the economy. Under the Senate plan, future immigrants would be evaluated more frequently based on their skills and employment prospects, which would help promote economic...