South Carolina Sen. Lindsey Graham sat down with The Wall Street Journal after addressing Republican activists Saturday in Nashua, N.H., and assessed his 2016 prospects and the debates over immigration policy and national security. Mr. Graham is currently “testing the waters,” which, in the parlance of the Federal Election Commission, means he is accepting donations of as much as $2,700-per-person to be used if he decides to run for president. Unlike many rivals who tend to stick to their talking points, the senator is becoming known for his unscripted and candid remarks on the campaign trail.