Jesse Jackson Jr. to resign: Brother Rep. Jesse Jackson resigned from Congress Wednesday, saying in a letter that he is cooperating with a federal investigation "into my activities" but blaming his health problems for his decision to step down just two weeks after his re-election. Jackson's letter to House Speaker John Boehner was his first acknowledgment of the ongoing corruption probe into his alleged misuse of campaign dollars. "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 said in the two-page letter dated Nov. 21. None of us is immune from our share of shortcomings or human frailties and I pray that I will be remembered for what I did right. Despite his admission of "my share of mistakes," Jackson said his deteriorating health was the reason he was quitting. He has been on medical leave since June while receiving treatment for bipolar depression. Against the recommendations of my doctors, I had hoped and tried to return to Washington and continue working on the issues that matter most to the people of the Second District. I know now that will not be possible," Jackson said in the letter. 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 as a member of the United States House of Representatives, effective today, in order to focus on restoring my health," Jackson wrote. The congressman could not be reached. Jackson, 47, won election this month while being treated at the Mayo Clinic in Rochester, Minn. and issued a statement on election night saying he would return to work once his doctors approved. "Once the doctors approve my return to work, I will continue to be the progressive fighter you have known for years," said Jackson, no longer a patient at Mayo. My family and I are grateful for your many heartfelt prayers and kind thoughts. I continue to feel better every day and look forward to serving you. He has not appeared in the House since June 8. Nor did he stage a campaign event -- or even run a TV Jackson advanced to the general election after defeating a one-term member of Congress, Debbie Halvorson, in a March primary. The next Congress will be sworn in Jan. 3 and Jackson would have been required to take the oath of office before being allowed to vote. News of the resignation on the eve of Thanksgiving, when Congress was not meeting and many Washingtonians were traveling, seemed to take even Jackson staffers by surprise. His press secretary, Frank Watkins, said Wednesday morning that he didn't know anything about a possible resignation. Watkins attributed the rumors to press speculation. Under Illinois law, Gov. Pat Quinn, a fellow Democrat, would call a special election to fill Jackson's 2nd District congressional seat, which extends from Chicago's South Side to Kankakee. Jackson's resignation, long suspected by political insiders, set off a scramble with as many as a dozen names of potential successors already surfacing. They range from political has-beens to up-and-comers in the south suburban district. Jackson has been under investigation by the House Ethics Committee for alleged improprieties related to his bid to win appointment in 2008 to the Senate seat that had been held by President Barack Obama. A Jackson emissary is alleged to have offered to raise up to $6 million in campaign funds for disgraced former Gov. Rod Blagojevich in exchange for the governor appointing Jackson to the Senate seat. Blagojevich is serving a prison term for corruption convictions including trying to sell or trade the Senate seat. After the March primary election, the congressman's aides belatedly announced his medical leave, which at first was blamed on "exhaustion." He is the son of the Rev. Jesse Jackson, the civil rights leader, and the husband of Chicago Ald. Sandi Jackson, 7th.