CHICAGO  — Rep. Jesse Jackson Jr. quietly resigned Wednesday, effectively ending a once-promising political career months after the civil rights icon’s son went on a mysterious medical leave while facing separate federal investigations.

Just two weeks after voters re-elected him to a ninth full term, Jackson sent his resignation letter to House Speaker John Boehner, citing his ongoing treatment for bipolar disorder and admitting “my share of mistakes.”

The House Ethics Committee is investigating his dealings with imprisoned ex-Illinois Gov. Rod Blagojevich, and for the first time Jackson publicly acknowledged reports of a new federal probe believed to be looking into his possible misuse of campaign money.

“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, adding “they are my mistakes and mine alone.”