By Richard Cowan and James B. Kelleher
WASHINGTON/CHICAGO (Reuters) - Representative Jesse Jackson Jr., who has been treated for bipolar disorder and is reportedly under investigation for possible misuse of campaign funds, resigned his seat on Wednesday, citing health reasons.
"My health issues and treatment regimen have become incompatible with service in the House of Representatives. Therefore, it is with great regret that I hereby resign ... effective today, in order to focus on restoring my health," the Chicago Democrat said in a letter to U.S. House Speaker John Boehner.
Jackson, the 47-year-old son of civil rights leader and former presidential candidate Reverend Jesse Jackson, also admitted to "my share of mistakes," in his two-page letter to Boehner, an Ohio Republican.
"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 and accept responsibility for my mistakes, for they are my mistakes and mine alone," Jackson wrote.
Jackson has been in Congress since 1995 and easily won re-election in a heavily Democratic district earlier this month despite his ailment and the ethics questions hanging over him.
His resignation was not expected to result in any changes in the political balance of power of the U.S. House, which is controlled by Republicans. Voters in Jackson's district will now have to hold a special election to fill the vacancy.
Illinois Governor Pat Quinn said he would propose a date for the election within five days.
"We know that Congressman Jackson is confronting health challenges, and our thoughts and prayers are with him and his family during this difficult time," Quinn said.
Jackson was treated for at least six weeks this summer at the Mayo Clinic in Rochester, Minnesota, for bipolar disorder, a psychological condition marked by extreme mood swings, and has been on medical leave since June.
He has also been the subject of a House ethics committee probe over an alleged bribe offered by a Jackson supporter in 2008 to then Illinois Governor Rod Blagojevich.
The bribe was said to be intended to entice Blagojevich to appoint Jackson to the U.S. Senate seat vacated by President Barack Obama. Jackson has admitted to lobbying for the seat, but denied knowing about any money offered to Blagojevich, who has since been convicted on corruption charges and imprisoned.
According to news reports citing unnamed sources, Jackson is also being investigated by the FBI over possible misuse of campaign money. The FBI has not confirmed the reports.
In his letter to Boehner on Wednesday, Jackson acknowledged a probe was underway and said he hoped it would not overshadow his years of public service.
"None of us is immune from our share of shortcomings or human frailties and I pray I will be remembered for what I did right," Jackson wrote.
Emails and calls seeking comment on his resignation made to Jackson's Washington, D.C., and Chicago offices, as well as to the office of Jackson's father, were not immediately returned.
Ironically, Jackson was sent to Congress in 1995 after winning a special election triggered by the resignation of Representative Mel Reynolds, a Democrat convicted of sexual assault, obstruction of justice and solicitation of child pornography.
Jackson, during his 17-year career in the House, was a reliable liberal vote, supporting increases in the minimum wage, the expansion of environmental regulations and gay rights and, in 2008, the bailout of the country's teetering financial system. He was also an early advocate of a strict timeline to withdraw U.S. troops from Iraq.
Reacting to Jackson's resignation, most fellow Democrats sidestepped his ethics problems and focused on his years of service in Congress.
Representative Nancy Pelosi, the Democratic leader, said Jackson had "presented a fresh perspective on how we work together" during his years on Capitol Hill.
Representative Bobby Rush, a former Black Panther who said he remembered Jackson when he was a "child crawling on the floor" of his parents' house, urged patience.
"He hasn't been charged, indicted or convicted of any breach of the law," Rush told reporters at an afternoon press conference in Chicago.
"Give the man a chance to go through his process."
(Additional reporting by David Bailey, Nick Carey and Thomas Ferraro; Editing by Cynthia Johnston and Todd Eastham)