He helped persuade Carrier to keep a factory in Indianapolis open in 2016, but the company still cut roughly half of the jobs at stake there. In 2017, he said Foxconn, a Taiwanese electronics supplier, would invest $10 billion to build a manufacturing complex in Wisconsin. The company was supposed to create 13,000 jobs — positions that have proved illusory. Mr. Trump’s 2018 assertion that “Chrysler is leaving Mexico and moving back to Michigan” was a stretch by any measure.

Workhorse, a small company based near Cincinnati, makes battery-powered pickup trucks, delivery vans, drones and aircraft, faces big obstacles in getting the Lordstown plant humming again with hundreds working the line. It has no experience in mass vehicle production, its shares recently traded for less than $1, and quarterly revenues were less than the price of one high-end sports car.

“This president is no stranger to grandiosity when it comes to job claims,” said Scott Paul, president of the Alliance for American Manufacturing, a partnership between employers and the steelworkers’ union. “Foxconn is in limbo and virtually no one believes it will live up to the billing.”

Senator Sherrod Brown, an Ohio Democrat, noted that Workhorse employs fewer than 100 people, compared with the thousands who worked for G.M. in Lordstown as recently as April 2018.

“It’s still too early to tell whether the sale is good news for workers,” he said in an interview.

It is not clear whether G.M. will strike a deal. The company said it was in discussions to sell the plant to a new business partly owned by Workhorse and headed by that company’s founder and former chief executive, Steve Burns.