". . . as my health has deteriorated, my ability to serve the constituents of my district has continued to diminish," Congressman Jackson wrote. "The constituents of the 2nd District deserve a full-time legislator in Washington, something I cannot be for the foreseeable future."
Jackson, 47, who has been on medical leave since June for bipolar disorder and depression, is under federal investigation for allegedly misusing campaign funds. He may be considering a deal in exchange for a plea in the federal case.
"During this journey I have made my share of mistakes. 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," he wrote.
Federal authorities have probed campaign spending by Jackson on personal items, including decorating his Washington, D.C. home, and a luxury watch for a female friend.
"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," Jackson wrote.
ABC7 has confirmed that the former congressman was in Chicago Wednesday night, but it was not clear where.
Jackson: "My mistakes [are] mine alone"
Jesse Jackson Jr.'s resignation letter reads like a plea bargain, and it's the first time the congressman has publically addressed his political problems. The words he uses to describe his legal situation are consistent with plea bargain language.
Jackson's attorney Dan Webb said Wednesday, "Mr. Jackson is cooperating with the investigation. We hope to negotiate a fair resolution of the matter but the process could take several months. During that time, we will have no further comment and urge you to give Mr. Jackson the privacy he needs to heal and handle these issues responsibly."
Jackson's wife, Chicago Alderwoman Sandi Jackson, is also under investigation for consultant fees received from her husband's campaign money.
He also wrote about the highlights during his 17-year Congressional career.
Visitors at the Jackson's Chicago home on Wednesday had no comment.
"Being a Jackson himself puts tremendous burden on him like no other," Mark Allen, a longtime friend who ran Jackson's first congressional campaign in 1995, said. "He was young enough to serve long enough to make history as the first black speaker of the house. So when you lose that level of history, that hurts."
Jackson is being treated at Mayo Clinic for bipolar disorder. He has been in and out of the clinic since June, and even in his absence easily won re-election earlier this month, telling voters he would be back at work soon as the "progressive fighter you have known for years."
Sympathy, support -- and sincerity?
Colleagues and constituents alike are showing sympathy for Jackson's illness, but some people wonder about the timing of it all.
"It's overdue, and I feel badly for him and his family," said one constituent near Jackson's office, which he shares with his wife, Chicago Alderwoman Sandi Jackson.
"I think it's a cop out, me personally, and he's got other things going on and he's trying to use that to hide what's really going on with him," said another.
Congressman Danny Davis and Bobby Rush spoke with Jackson during his leave of absence.
"I don't believe that you could convey the genuine feeling that I saw coming from him as he talked about his hopes, his aspirations," U.S. Rep. Danny Davis said.
"I don't think anybody was duped," Congressman Rush said. "I don't think he knew what was going to happen."
In 2008, Jackson was also linked to former Gov. Rod Blagojevich's plan to sell a U.S. Senate seat to the highest bidder. Blagojevich was convicted on corruption charges. Jackson was never charged in the case, but the House Ethics Committee is investigating the allegations.
Jackson's leave of absence came as Raghuveer Nayak, a Blagojevich fundraiser, was arrested on unrelated medical fraud charges.
Special Election to replace Jackson in Congress
According to law, Gov. Pat Quinn has five days following the resignation to set the date for a special election to replace Jackson in Congress.
"That five days would expire on Monday and by Monday we'll have the schedule prepared," Gov. Pat Quinn said Wednesday.
The election has to be held within 115 days of the Governor's announcement.
"We don't have a lot of time to work on this, but if we have our way, [it] will be done on the existing dates already set in February and April," Cook County Clerk David Orr said.
Orr is referring suburban elections already scheduled in Cook, Will and Kankakee counties: the state primary on February 26, 2013, and the general election on April 9. Holding the special election for Jackson's seat on those dates would offset the overall cost. But it will also require judiciary action because of state-required deadlines. Orr said he and his team have been working on the possibility of a special election since the Jackson rumors started swirling.
"The only new thing is Jackson made his resignation today," Orr said. "We've been preparing."
There is no election for Chicago in the spring, so there will be additional costs to the Chicago Board of Elections. So who may run?
"I think we're hearing upwards of 12 people probably throwing their hats in the ring for this campaign," Delmarie Cobb, political consultant.
Political constituent Delmarie Cobb said candidates who want to run for the 2nd Congressional District of Illinois could run into problems raising the money, especially so soon after the General Election. They'd also only have a few weeks to campaign.
"It's going to be the candidate who has the highest visibility who will be able to maybe win. So you've got to have name recognition and visibility to win this seat," Cobbs said.
Jackson's post-election resignation means one less Democrat in the House for the next six months. Politically, Governor Quinn wants the seat filled as soon as possible.
"We want to make sure Illinois is fully represented," Quinn said.
Chicago Mayor Rahm Emanuel issued a statement on Wednesday, "While I'm sure this was a difficult decision for Congressman Jackson, now is the time to look forward. The residents of the 2nd Congressional District will now have an opportunity to choose their next leader to fight for all of us in Washington, DC. My thoughts and prayers and with the Jackson family and I wish Jesse a healthy recovery."