WASHINGTON — The job approval rating of embattled Sen. Bob Menendez (D-NJ) tanked in a new poll released yesterday as scrutiny lingers over his relationship with a huge Democratic campaign donor.

Four in 10 New Jersey residents disapprove of the job Menendez is doing, a 15-percentage-point drop from a poll taken last month, according to Quinnipiac University.

Menendez has acknowledged contacting the feds regarding an $8.9 million Medicare dispute on behalf of Democratic donor Salomon Melgen, a Florida eye doctor.

The FBI is also probing whether Menendez solicited underage prostitutes.