As Mrs. Clinton began her 2016 campaign for the presidency, Hugh Rodham and Roger Clinton had faded from public view, but Tony Rodham emerged as a controversial figure. A government investigation in March found that GreenTech, which sought green cards for its Chinese investors through an American government program, had received special treatment in the handling of its visa applications. The report described instances when Mr. McAuliffe and Mr. Rodham contacted an official from the Department of Homeland Security to complain about the pace of the visa process.

Mr. Rodham’s unsuccessful pursuit of housing contracts in Haiti, which has not previously been reported, raised new questions.

As Mrs. Clinton campaigns, she speaks fondly of her brothers. At a stop in Iowa, she recalled them working together at her father’s drapery business. Her official campaign biography prominently mentions them.

“She loves her family more than anything,” said Nick Merrill, a spokesman for Mrs. Clinton. “Her brothers have always been there for her, and she will always be there for them. Each, though, have their own lives, their own jobs, their own ups and downs.”

As the youngest of three children, Tony Rodham has lived in the shadow of his sister. He never finished college, and he worked at a variety of jobs — as a prison guard, private detective and at the Democratic National Committee — until after the Clintons were in the White House, when he became a consultant and deal broker. He was once married to Nicole Boxer, the daughter of Senator Barbara Boxer of California.

He lives with his second wife, Megan, and two young children in a large house on a hill in Vienna, Va., a suburb of Washington. He declined to speak to a reporter who went to his door one afternoon in April, and he did not respond to other messages seeking comment for this article.