The morning was rainy and glooming in Augusta, Maine, but the mood couldn’t be sunnier inside the opulent historic residence known as the Governor Hill Mansion. “Centrists are dead!” state Representative Valli Geiger declared in the stately dining room. “I can’t believe it!” state Representative Jan Dodge enthused. The ebullient legislators were among the dozen-plus state officials gathered on April 30 to endorse Democratic U.S. Senate candidate Graham Platner, a 41-year-old oyster farmer and