In a moment that blurs the familiar lines of American partisan life, Democratic Senator John Fetterman of Pennsylvania appeared by video at the Republican National Convention to endorse his GOP colleague Dave McCormick, praising President Trump and declaring himself a 'commonsense Democrat' who rejects extremism. The gesture, rooted in shared loyalty to Pennsylvania's steel industry, is less a defection than a signal — one that raises enduring questions about where ideological conviction ends and party identity begins. Fetterman's appearance asks something the American political system rarely