Donald Trump sparked a showdown with Barack Obama after calling the former president a “jerk” during his North Carolina campaign stop. RadarOnline.com can reveal the Republican candidate ripped into Obama for being “careless” just as the Democrat threw a punch at Trump during a fiery Detroit rally on Tuesday, reigniting their bitter feud. The MAGA enthusiast, 78, said: “I think he’s a real jerk because I’ve watched him campaign over the last couple of days. “Over the last couple of days I’ve watched him campaign. What a divider he is. He divides this country. He couldn’t care less, him and his…