PHILADELPHIA — At a rally earlier this month, former President Donald Trump seemed to relish describing the grisly details of murders in Philadelphia. The city has “become a killing field,” he told thousands of supporters. At the same event in Northeast Pennsylvania, Republican Senate nominee Mehmet Oz pointed to Philly’s homicide rate and emphasized his endorsement from the Fraternal Order of Police, the main police union. “I know and believe we can have safe city streets,” he said. Two months before Pennsylvania’s crucial elections, crime has taken up a central role in Republicans’ campaigns…