"The reason I'm leaving at the end of this congressional session is solely for professional considerations ...and my preference is to find a job with expanded responsibilities," said Goffman, reading from a statement. "It absolutely in no way reflects my views on Sen. Lieberman's support for Sen. McCain."
Goffman, a Democrat who has worked for Lieberman since 2006, declined to say whether he agreed with the Connecticut independent's decision to attack Barack Obama's experience during a speech at the GOP convention.
"I'd prefer to keep those views to myself," he added.