A defiant Sen. Robert Menendez declared, “I am not going anywhere,” Friday night as the Justice Department prepares to charge the New Jersey Democrat with corruption counts over allegations he used his office to help a Democratic donor.

The Justice Department is expected to bring criminal charges against him in the coming weeks, following a federal grand jury purportedly finding Menendez took official action on behalf of himself and that he received gifts from wealthy friend Dr. Salomon Melgen.

The government also alleges that Menendez and ‎his staff advocated on Dr. Melgen's behalf in a meeting among the senator, Nevada Democratic Sen. Harry Reid and then-Health and Human Services Secretary Kathleen Sebelius.

The government also points to emails between former Menendez chief counsel Kerru Talbot and a staffer with Customs and Border Patrol in ‎which Talbot purportedly asked the agency not to donate screening equipment to the Dominican Republic, but instead to allow a private contractor controlled by Melgen to provide that equipment.

Menendez said at a press conference Friday, about four hours after the reports of the charges surfaced, that he had “always conducted (his self) appropriately and in accordance with the law. I fight for things I believe important … and for the people of our country,” he also said. “That’s who I am. I am not going anywhere.”

Menendez took no questions from reporters, saying that because of the “ongoing inquiry” he could not make any additional comments. His office has not confirm the grand jury investigation and forthcoming charges but has defended the senator's conduct.

In a statement, Menendez spokeswoman Tricia Enright said: "As we have said before, we believe all of the senator's actions have been appropriate and lawful and the facts will ultimately confirm that.

“Any actions taken by Senator Menendez or his office have been to appropriately address public policy issues and not for any other reason."

Attorney General Eric Holder has also declined to comment on the case when asked by Fox News. And President Obama ignored shouted questions by reporters Friday as he departed from Marine One following a trip to South Carolina.

Menendez has been a leading critic of the direction of current diplomatic talks with Iran over its nuclear program and has helped draft legislation meant to check the administration's power to negotiate a deal.

As the top Democrat on the Senate Foreign Relations Committee -- and a Cuban-American lawmaker -- he also has criticized the administration's efforts to normalize ties with Cuba.

According to CNN, which first reported Justice Department charges, investigators looked at a plane trip the senator took as Melgen's guest to the Dominican Republic.

They also looked at how Menendez allegedly advocated for him with Medicare officials who accused him of over billing and allegedly pushed his friend's business interests in the Dominican Republic.

The New Jersey Law Journal, late last month, also reported on court documents in the case, which reportedly were posted by accident for a brief time. The publication said an appeals court has ordered a hearing into whether Menendez' aides can be compelled to testify to a grand jury in the case. The Law Journal, citing the court documents, said the case revolves around the billing dispute Melgen had with Medicare officials and the donor's deal to sell port-screening equipment to the Dominican Republic.

Enright said Friday that Melgen is one of Menendez' closest friends but they cannot specifically address the claims.

"The two have spent holidays together and have gone to each other's family funerals and weddings and have exchanged personal gifts. As has been reported, the start of this investigation is suspect," she said. "We know many false allegations have been made about this matter, allegations that were ultimately publicly discredited. We also know that the official investigation of this matter is ongoing, and therefore cannot address allegations being made anonymously."

Various allegations indeed have swirled around the New Jersey lawmaker, including that he solicited prostitutes in the Dominican Republic -- allegations that have not been substantiated.

The Justice Department's record of going after high-level lawmakers is mixed.

They have won convictions against several House members, including former Republican Rep. Rick Renzi and former Democratic Rep. Bill Jefferson. But the late Sen. Ted Stevens, R-Alaska, had his conviction vacated over prosecutorial misconduct. They also never went after Alaska Rep. Don Young, R-Alaska, despite claims they were considering it years ago.

Fox News' Chad Pergram, Jake Gibson and Jodie Curtis and The Associated Press contributed to this report.