CHICAGO (AP) -- Rep. Jesse Jackson Jr., a once-rising political star who has been on a months-long mysterious medical leave for bipolar disorder while facing separate federal investigations, resigned from Congress Wednesday, citing his health problems.
Jackson's resignation, just two weeks after voters re-elected him to a ninth full term, comes amid a House Ethics Committee investigation into his dealings with imprisoned ex-Illinois Gov. Rod Blagojevich and reports of a new federal probe into possible misuse of campaign money.
In his resignation letter to House Speaker John Boehner, Jackson admits "my share of mistakes" and, for the first time, publicly acknowledges that he is the subject of an ongoing federal investigation.
"I am aware of the ongoing federal investigation into my activities, and I am doing my best to address the situation responsibly, cooperate with the investigators, accept responsibility for my mistakes," he wrote.
Jackson added: "They are my mistakes and mine alone."
Jackson, 47, disappeared in June, and it was later revealed that he was being treated at the Mayo Clinic for bipolar disorder and gastrointestinal issues. He returned to his Washington home in September but went back to the clinic the next month, with his father, the Rev. Jesse Jackson, saying his son had not yet "regained his balance."
Attempts by The Associated Press to locate Jackson were unsuccessful Wednesday, and family members either declined to comment or could not be reached.
Jackson was easily re-elected Nov. 6 to represent his heavily-Democratic district, even though his only communication with voters was a robocall asking them for patience. He spent election night at the Mayo Clinic but later issued a statement thanking his supporters and saying he was waiting for his doctors' OK before he could "continue to be the progressive fighter" they'd known for years. He left the clinic a second time earlier this month but has not spoken publicly since.
His return to the clinic in October came amid reports, first by the Chicago Sun-Times citing anonymous sources, that he faced a new federal investigation into potential misuse of campaign funds. An FBI spokesman in Washington, Andrew Ames, has told The Associated Press he could neither confirm nor deny the existence of a federal investigation into Jackson.
In his resignation letter, Jackson cites his health issues as the reason for his departure from Congress and says he hopes he is remembered on the balance of his work.
"The constituents of the (2nd) District deserve a full-time legislator in Washington, something I cannot be for the foreseeable future. My health issues and treatment regimen have become incompatible with the House of Representatives," Jackson wrote.
Jackson took office in 1995 after winning a special election. Voters in the district have said Jackson's family name and attention to local issues have been the reasons for their support. He has easily won every re-election since taking office and brought home close to $1 billion in federal money for his district during his tenure.
He began his career in Washington with a star power that set him apart from his hundreds of House colleagues. But his resignation ends a once-promising political career that was tarnished by the allegations that he was involved in discussions about raising campaign funds for then-Gov. Blagojevich in exchange for an appointment to President Barack Obama's vacated U.S. Senate seat.
The House Ethics Committee is investigating reports of those allegations, which Jackson has denied. After the allegations surfaced, he cut back drastically on his number of public appearances and interviews. Blagojevich is now in federal prison after being convicted of trying to sell the seat, among other things.
The timing of Jackson's leave in June and the way it was handled also has invited scrutiny. It was announced just after a former fundraiser connected to the Blagojevich allegations was arrested on unrelated medical fraud charges.
Illinois Gov. Pat Quinn, a Democrat, has five days to schedule an election to replace Jackson after he receives official notice, and the election must be held within 115 days, according to election officials.
The vacancy left by Jackson's departure creates a rare opportunity for someone else to represent his district, which is made up of South Side Chicago neighborhoods, several southern suburbs and some rural areas. Even this year, when Jackson was absent during the crucial final months of campaigning, he easily defeated two challengers on the ballot.
Henry C. Jackson reported from Washington. Associated Press Special Correspondent David Espo in Washington contributed to this report.