The Democratic senator, whose trial starts Wednesday, is charged with using his power to do favors for Florida ophthalmologist Salomon Melgen, who is accused of overbilling Medicare, AP reported.
According to prosecutors, the doctor repaid Menendez with "a lavish lifestyle that included private jet rides and vacations in Paris and the Caribbean."
Prosecutors also say Melgen allowed Menendez to make ten trips to the Dominican Republic on the Florida doctor's private jet, and then stay at the doctor's luxury resort for free.
Melgen also supposedly paid the bill for a suite in a five-star hotel in Paris where Menendez and a guest stayed in 2010.
The charges also state that Melgen gave more than $750,000 to political institutions back up the senator's re-election.
In return for all of these favors, prosecutors are claiming that Menendez and his staff convinced Department of Health and Human Service regulators to brush aside claims that Melgen overbilled Medicare by almost $9 million.
Menendez claims that he was just being a good friend to someone he's known for many years. When the charges were filed in 2015, Menendez said, "Prosecutors at the Justice Department don't know the difference between friendship and corruption," NBC reported.
The senator's lawyers are also arguing that none of what Menendez did is considered corruption under federal bribery law, because Menendez never promised Melgen he would take any particular steps in exchange for the favors.
However, according to the US legal code on bribery, it is illegal to "directly or indirectly, corruptly give, offer or promise anything of value to any public official or person who has been selected to be a public official, or offers or promises any public official or any person who has been selected to be a public official to give anything of value to any other person or entity, with intent."
This is not the first time Melgen has been accused of fraudulent behavior. In April, Melgen was convinced of defrauding Medicare. His sentencing has been delayed until after the Menendez trial. If the 62-year-old is found guilty, he could face 20 years — potentially the rest of his life — in prison.
And if Menendez is convicted, he would obviously have to step down from his position. His successor would be appointed by New Jersey's current Republican governor, Chris Christie, giving Republicans an extra voice in the Senate and perhaps shifting the political climate.