Charlie Rangel is defending himself against the 13 ethics charges he is facing, tweeting to supporters that he has found some "mistakes" but that he "won't stop fighting until I've had a fair and open hearing."

Rangel, 80, could face a rare public ethics trial in September -- leading up to the midterm elections -- if a settlement is not reached. Democrats urged Rangel to settle the charges, fearing the negative effects that a public trial of one of the longest-serving members of its caucus could have.

Rangel is being investigated for his use of four rent-controlled apartments in New York City, using congressional letterhead to raise money for a New York City College center for public service bearing his name, not reporting income and assets, and preserving a tax loophole for a group that donated to the City College center.

"The undisputed evidence in the record -- assembled by the Investigative Subcommittee over its nearly-two-year investigation -- is that Congressman Rangel did not dispense any political favors, that he did not intentionally violate any law, rule or regulation and that he did not misuse his public office for private gain," read a statement Rangel submitted to the House Ethics Committee.



Also facing investigation is Congresswoman Maxine Waters for charges that she helped a bank, where her husband owned stock, gain a federal bailout. Waters has denied any wrongdoing, saying that she was advocating for minority-owned banks during the financial meltdown.

Some Democrats have returned Rangel's donations while others have called for him to resign. President Barack Obama did not provide strong words of support for the congressman who has served his Harlem district for 40 years.

"I think Charlie Rangel served a very long time and served his constituents very well, but these allegations are very troubling," Obama told CBS Evening News.

"He's somebody who's at the end of his career. Eighty years old. I'm sure that what he wants is to be able to end his career with dignity. And my hope is that it happens."