To watch Ted Cruz speak at a gathering of religious conservatives in Washington Friday was to more fully grasp why the Republican senator from Texas could win the Iowa caucus next year. In two words: religious liberty. Cruz has only one rival in the Republican field — former Arkansas Gov. Mike Huckabee — who raises the issue as aggressively. But between the two of them, Cruz has a reputation as a fighter, having tangled repeatedly with GOP leadership in Congress on a host of issues since he was elected in 2010. And the grassroots wants a brawler. Iowa conservatives, who...