A candidate for mayor of a violence-wracked city in Mexico has been killed just as she began campaigning. Two authorities in the north-central state of Guanajuato said candidate Bertha Gaytán was shot to death on a street in a town just outside the city of Celaya. Mayorships in Mexico often included smaller surrounding communities. The authorities were not authorized to be quoted by name. Video of the scene posted on social media showed a small procession of people shouting "Morena!" — the name...