YPSILANTI TOWNSHIP, Mich. — Pandemic politics shadowed President Donald Trump’s trip to Michigan on Thursday as he highlighted lifesaving medical devices, with the president and officials from the electoral battleground state clashing over federal aid, mail-in ballots and face masks.

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.

All of the Ford executives giving Trump the tour were wearings masks, the president standing alone without one. At one point, he did take a White House-branded mask from his pocket and claim to reporters he had worn it elsewhere on the tour, out of public view.

“I did not want to give the press the pleasure of seeing it,” Trump said.

For a moment, he also teasingly held up a clear shield in front of his face. A statement from Ford said that Bill Ford, the company’s executive chairman, “encouraged President Trump to wear a mask when he arrived” and said the president wore it during “a private viewing of three Ford GTs from over the years” before removing it.