Senator Rand Paul, a conservative Republican whose vote is being courted by supporters of a broad U.S. immigration bill, said on Sunday he is open to voting for the measure but wants changes, including tougher border security requirements. Paul, who has hinted at an interest in running for president in 2016, in March backed the concept of a path to citizenship for undocumented immigrants that is at the heart of a comprehensive immigration bill under consideration in the U.S. Senate. But Paul, of Kentucky, has also criticized some elements of the bill, saying it should provide a mechanism for assuring...