A Florida doctor is at the center of the corruption case against New Jersey's Sen. Robert Menendez.

Dr. Salomon Melgen, a donor to the Democratic party and its candidates, has been friends with Sen. Menendez for 22 years.

Melgen is accused to trading money for influence with the senator.

"I'm angry because prosecutors at the Justice Department don't know the difference between friendship and corruption and have chosen to twist my duties as a senator and my friendship into something that is improper," Menendez said at a news conference.

The FBI alleges that Melgen wanted the senator to advocate on his behalf concerning Medicare billing and more.

The 61-year-old opthalmologist graduated from medical school in the Dominican Republic, but later moved to the United States and trained at Harvard to become a top-flight surgeon, online biographies say.

He subsequently made millions of dollars with a private practice in South Florida. Investigators claim he has used some of that money to buy influence from politicians.

Melgen has also donated money to Minnesota Democratic Sen. Amy Klobuchar. She says she will return the money.