(CNN) - His son, the former Rep. Jesse Jackson Jr., spiraled from a position of promise to one of disgrace over the past year. It began with his mysterious disappearance from the halls of Congress, word of mental health issues, his resignation, and then a guilty plea to misusing campaign funds.
The elder Jackson said in an interview Wednesday on CNN's "The Situation Room" that this was a sad, but "perhaps not the last chapter" of his son's service.
"He's still battling with bipolar disorder. He's now spending his time on his medical regimen and scribbling out notes how to help other people with bipolar disorder," Jackson said.
His son's counsel for others suffering with mental health issues is one way his son "is still serving," Jackson said.
The congressman's absence from Washington drew questions and eventually acknowledgement from his office that he suffered from mental health and gastrointestinal issues and was in treatment at the Mayo Clinic.
Jackson, a Democrat, went on to win re-election to a 10th term in his Illinois district without making any campaign appearances, save a recorded, automated phone call to voters asking for their support and explaining "a series of events came together in my life at the same time and they've been difficult to sort through."
He resigned in late November, citing his health concerns.
A week ago, he pleaded guilty to misusing $750,000 in campaign funds over the past seven years. Prosecutors said he used campaign credit cards to buy expensive trinkets with ties to former U.S. presidents, the late singer Michael Jackson, the Rev. Martin Luther King Jr., Malcolm X and martial artist Bruce Lee.
His wife also plead guilty to a separate count of filing false tax returns.
As he left the courthouse in Washington, the younger Jackson said that he was sorry to have “let everybody down."
His father told CNN that it was a painful moment. “It's a sad chapter, perhaps not the last chapter," he said.
"He has been quite contrite, accepted his responsibility. He did not lean on his sickness, his bipolar disorder, which has been considerable," Jackson said.
The former presidential candidate said his son "is standing up with dignity, fighting these odds, and … I love him so much, and [am] so very proud of him yet."
Jackson Sr. spoke on the day a statute of civil rights pioneer Rosa Parks was unveiled in Congress. His son had sponsored the legislation behind the statue.
Jackson, himself a civil rights leader, was with King on the day he was assassinated in Memphis in April 1968.
– CNN's Gregory Wallace and Carol Cratty contributed to this report