A look at 15 unexpected resignations throughout history

In November 2012, Rep. Jesse Jackson Jr., D-Ill., resigned from Congress, citing health reasons but also acknowledging an ongoing federal investigation, USA Today reported at the time.

"Over the past several months, as my health has deteriorated, my ability to serve the constituents of my district has continued to diminish," Jackson said in a letter to House Speaker John Boehner. "I am aware of the ongoing federal investigation into my activities and I am doing my best to address the situation responsibly, cooperate with investigators and accept responsibility for my mistakes, for they are my mistakes and mine alone."

The resignation came a few months after Jackson took a medical leave of absence for "exhaustion."

Jackson reached a plea agreement with prosecutors investigating his alleged misuse of campaign funds on Feb. 8, 2013, a USA Today article said.