Puerto Rico, a self-governing commonwealth whose residents are U.S. citizens, has already voted three times (1967, 1993 and 1998) against becoming the 51st U.S. state. But Congressional Democrats, hoping to add to their numbers in Congress, keep pushing for statehood. Late last month, the House voted 223 to 169 to begin yet another attempt to have the island join the union. The latest bill would require Puerto Ricans first to vote on whether to continue their commonwealth status. If a majority vote for a change, the people would then be presented with a range of choices, including statehood, full independence,...