Two months before Sgt. La David T. Johnson died in an ambush in Niger, he told his sister in an hourlong video chat that he was ready to come home. He wanted to see his children again and return to his wife, then four months pregnant with their third child.

“He was ready,” said Torneisha Ghent, 24, who along with her brother grew up in Carol City, a neighborhood in north Miami-Dade County.

But Sergeant Johnson remained committed to his role as an Army mechanic serving the 3rd Special Forces Group as part of a mission to train African troops in the fight against terrorism. He told friends and family he wanted to help his team. He also needed the money to buy a home for his growing family.

Ms. Ghent would never see her brother again. Weeks after their last exchange, Sergeant Johnson’s family learned that he had disappeared in a firefight. Days later, they learned of his death after an ambush. And then came the controversy over President Trump’s call to Sergeant Johnson’s widow, Myeshia Johnson, and the swirling feud that followed involving the president, his chief of staff, John F. Kelly, Ms. Johnson and Representative Frederica S. Wilson, Democrat of Florida, over what was said in the call. Yet many who knew the slain soldier now lament that Sergeant Johnson’s story has gotten lost amid the flurry of criticism and accusations.