Mayors, who are traditionally among the most popular political leaders in France, are under attack like never before. Opposition to immigration is a driving factor, spearheaded by tiny extreme-right parties that are frequently supported by national leaders Some of the threatening letters to Jean-Yves Rolland, mayor of Callac. AP The mayor of a small resort town on the Atlantic coast of France resigned, closed his medical practice and moved away after his house and two cars were set on fire. The arson followed months of death threats over plans to relocate a refugee center near a school. More than 150...