But the Twitter account that prompted the article was not his sister. It was a fake profile run by Josh Hall, a 21-year-old food-delivery driver in Mechanicsburg, Pa.

“I was like, ‘Oh, my goodness. He actually thinks it’s his sister,’” Mr. Hall, a fervent Trump supporter, said in an interview last week.

It was a surreal coda to nearly a year of deception for Mr. Hall. Since February, he had posed as political figures and their families on Twitter, including five of the president’s relatives. He had pretended to be Robert Trump, the president’s brother; Barron Trump, the president’s 14-year-old son; and Dr. Deborah L. Birx, the White House coronavirus response coordinator. The accounts collectively amassed more than 160,000 followers.

Using their identities, he gained attention by mixing off-color political commentary with deranged conspiracy theories, including one that the government wanted to implant Americans with microchips, and another that John F. Kennedy Jr., who died in a plane crash in 1999, was alive and about to replace Mike Pence as vice president.