CHICAGO (CBS) — Just two weeks ago, Jackson was re-elected to the Congress for a tenth term. He had been there for 17 years.

His career in Congress ended Wednesday with his resignation over major health issues and a lingering federal investigation, a surprise end to the career of a man who was once considered a serious candidate for mayor of Chicago, and possible future U.S. Senator.

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Ironically, his political career started when former Congressman Mel Reynolds’ career ended in disgrace, after he was forced to resign over his conviction on sexual assault charges stemming from a relationship with a 16-year-old campaign volunteer.

Jackson joined a crowded field of prominent Democrats to run for Reynolds’ seat, running as the only candidate to support then-Gov. Jim Edgar’s proposal to build a third regional airport in Peotone — a plan that would become the signature of Jackson’s career.

“Today, I appeal to you to let me be that public servant who you can believe, upon whom you can rely, and upon whom you can trust,” Jackson said as he first ran for office in the special election in 1995 to replace Reynolds.

He won that race easily, and his congressional career began with such hope.

“I want to defend the defenseless. I want them to dream again and stop recycling nightmares,” he said as he was sworn in.

Throughout his 17 years on Capitol Hill, he pushed for equality in education, health care, and voting rights. And he relentlessly supported a third regional airport to boost Chicago’s south suburbs.

In 2008, at the Democratic National Convention, Jackson tried to become a unifier within his own party, hugging several political rivals at the time, and arranging a famous hug between two heated adversaries: House Speaker Mike Madigan and then-Gov. Rod Blagojevich.

However, then-U.S. Sen. Barack Obama’s ultimate ascent to the presidency was the beginning of Jackson’s political descent.

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His name soon surfaced as a player in the federal corruption case against Blagojevich. Jackson has denied sending emissaries to offer Blagojevich campaign cash for an appointment to Obama’s empty Senate seat.

“I reject and denounce pay-to-play politics, and have no involvement whatsoever in any wrongdoing,” Jackson said in December 2008.

But by 2010, a congressional ethics probe had uncovered an affair Jackson Jr. had with a restaurant hostess.

He insisted no federal funds or campaign funds were used to fly his mistress to and from D.C., but investigations into possible misuse of campaign funds continued, and by the 2012 primary election, Jackson was facing stronger opposition.

Although he again won handily, he said he’d never run so hard for re-election before.

He was all smiles at his victory rally after the March primary, but just three months later he dropped out of sight, taking a leave of absence from Congress.

By August, it was revealed Jackson was suffering from bipolar disorder. Since June, he has been seen only in photos taken at the Mayo Clinic, and later outside his home in Washington, D.C.

In September, he was seen closing the blinds at his D.C. home, and in late October, constituents heard from Jackson in a robocall to residents of his district.

“After my family, my constituents are the most important people in the world to me. I will always act in your best interests,” he said in his message to voters.

Jackson is a licensed attorney, though not a practicing lawyer. If the ongoing federal investigation of his use of campaign funds leads to a guilty plea to a felony, or if he’s convicted of a felony at trial, he’d lose his license to practice law, and be ineligible to run for state or local office in Illinois.

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His future clearly is uncertain.