Reid adds: "But that's what investigations are all about."
Menendez's office last week disclosed that he reimbursed the donor, Dr. Salomon Melgen, for the full cost of two trips that Menendez took in 2010 to the Dominican Republic.
The FBI searched the eye doctor's office in a raid that took place on Tuesday night and early Wednesday.
Reid said on ABC's "This Week" that he's comfortable with Menendez serving as the chairman of the Senate Foreign Relations Committee.
