Trump visited Ypsilanti, outside Detroit, to tour a Ford Motor Co. factory that had been repurposed to manufacture ventilators, the medical breathing machines governors begged for during the height of the COVID-19 pandemic. But his visit came amid a long-running feud with the state’s Democratic governor and a day after the president threatened to withhold federal funds over the state’s expanded vote-by-mail effort. And, again, the president did not publicly wear a face covering despite a warning from the state’s top law enforcement officer that a refusal to do so might lead to a ban on his return.