New Jersey Senator Robert Menendez heads back to Washington Monday as questions over his relationship with Dr. Salomon Melgen, a long time friend and major campaign donor from Florida, continue to attract scrutiny.

Last week the FBI raided Melgen's offices and a member of the Senate Ethics panel confirmed it was reviewing the matter. 

But Brigid Harrison, a professor of law and Politics at Montclair State University, says the Melgen matter is no threat to Menendez's career.

"Nothing that he has done to date has caused him any serious deleterious impact on his political career including the time which US Attorney Chris Christie was in that position and was investigating him," Harrison says.

In 2007 the US Attorney's office under Christie opened up a probe into Menendez's renting of a building he owned to an anti-poverty non-profit that received millions of dollars in federal funding. 

Subsequently, Menendez received written confirmation from the Department of justice that the matter had been dropped and that no criminality had been found.

Professor Harrison notes that over the weekend, Menendez's Senate colleagues, including Majority Leader Harry Reid, came forward to vouch for him.

On Friday, Governor Christie had only words of praise for the Senator when both men addressed the annual New Jersey Chamber of Commerce "Walk to Washington" banquet.

Through a spokesperson, Menendez has denied published reports he improperly lobbied on behalf of Melgen's interest in a Dominican Republic Port security contractor.

Last month, Senator Menendez paid back $58,000 to cover the cost of two private flights to the Dominican Republic in 2010 on Melgen's provate jet.

Menendez's disclosure and payment only came after New Jersey State Senator Samuel Thompson, who is also a Republican County chair, filed formal charges against Menendez last year.

"Well I had to file an ethics complaint with the Senate Ethics Committee back in October. I had information regarding flights that had been provided to him by this doctor down in Florida on his private jet," Thompson told WNYC.

A spokesman for Senator Menendez says the Senator has done nothing wrong and that his failure to disclose the flights two years ago was just an oversight.

Speculation surrounding the Menendez-Melgen relationship climaxed at around the same time Menendez was selected to chair the Senate's powerful Foreign Affairs Committee last week.