In a moment that unsettled the familiar boundaries of American party politics, Democratic Senator John Fetterman of Pennsylvania appeared by video at the Republican National Convention to offer praise for Donald Trump — unannounced, unexpected, and without the blessing of his party. The appearance did not emerge from nowhere: Fetterman had long cultivated an image as an independent voice for working-class Pennsylvanians, yet this crossing of a symbolic threshold invites deeper questions about what holds political identity together when conviction and allegiance begin to pull in different direc