CHICAGO — A few years ago, the political career of Representative Jesse L. Jackson Jr. was soaring.

His appeal had long since crossed race and class lines — a Barack Obama before anyone heard of Barack Obama — and he seemed destined for a political future that could reach higher and wider than that of his father, the civil rights leader and former presidential candidate whose name he shared.

But Mr. Jackson’s prospects have tumbled precipitously since the end of 2008. Most recently, Mr. Jackson, 47, has been absent from Congress since June 10, and in the last few weeks his office has released three brief statements, which seemed to set off as many questions as they answered. The latest, on Wednesday night, said that he was receiving “intensive medical treatment at a residential treatment facility for a mood disorder” and is expected to recover.

Last week, his office had said he had grappled with “certain physical and emotional ailments privately for a long period of time” — a more dire, if mysterious, assessment than its initial explanation, a week before, that he was dealing with exhaustion.

The disclosures, absent details, have set off waves of speculation here and in Washington about the precise nature of Mr. Jackson’s ailment, his location and, four months before his presumed re-election to Congress, his political future. It has left his father, the Rev. Jesse Jackson, who this week is hosting his annual Rainbow PUSH Coalition national conference about how to combat poverty and unemployment, fending off relentless questions about his eldest son.