Mavericky Sen. John Fetterman slapped down calls for him to become a Republican due to his penchant for breaking ranks with Democrats, arguing that he’d be “terrible” as a GOPer. The hulking, hoodie- and shorts-wearing senator was adamant that he hasn’t changed, but his party has, and that he’s refused to lurch to the left on issues such as the border and avoiding government shutdowns . “These once-common views have become increasingly toxic in the Democratic Party, a result of catering to the fringe and agitated parts of our base,” Fetterman candidly wrote in a Washington Post op-ed Thursday. Sen. John Fetterman defended his Democratic bona fides and vowed to remain an independent voice in the Senate. REUTERS “My values have not changed, and I have always turned to those kinds of ideals that defined being a Democrat,” he added.…