Florida neurologist Marc Swerdloff was taken aback when one of his patients with advanced dementia voted in the 2000 presidential election. The man thought it was 1942 and Franklin D. Roosevelt was president. The patient's wife revealed that she had escorted her husband into the booth. "I said 'Did he pick?' and she said 'No, I picked for him,' " Swerdloff said. "I felt bad. She essentially voted twice" in the Florida election, which gave George W. Bush a 537-vote victory and the White House. As swing states with large elderly populations such as Florida gear up for another presidential...