The case of a Mexican man scheduled to be executed on Thursday in Texas threatens to disrupt U.S. diplomatic relations abroad and creates a politically volatile dilemma for Republican Gov. Rick Perry, who is considering a run for president. Unless Perry or the U.S. Supreme Court intervenes to stay the execution, Texas plans to execute Humberto Leal Jr. at 6 p.m. Central Time for the 1994 murder of 16-year-old Adria Sauceda. The International Court of Justice ruled in 2004 that the United States violated the rights of Leal and more than three dozen other Mexican nationals on death row because...