Sen. Robert Menendez (D-N.J.) was indicted on federal corruption charges Wednesday, accused of using the influence of his office to advance the business interests of a longtime friend and political supporter in exchange for luxury gifts, lavish vacations and more than $750,000 in campaign donations.​

Federal prosecutors laid out the charges in a 14-count indictment charging Menendez with using his office to help Salomon Melgen, a ­Florida-based eye doctor with whom Menendez had maintained a long personal and political friendship. Menendez intervened on Melgen’s behalf in at least two disputes, one with federal regulators over Medicare charges and the other involving a bid by Melgen to secure a ­port-security contract in the Dominican Republic, according to the indictment.

Prosecutors say that over a seven-year period, Menendez relied on Melgen for free private-jet flights to weekend getaways at resorts in Florida, the Dominican Republic and Paris.

Menendez has repeatedly denied any wrongdoing. He was defiant Wednesday night before a boisterous crowd of supporters, saying that Melgen’s gifts were a result of friendship dating to the early 1990s and not in exchange for political favors.

During a March 6 news conference, Sen. Robert Menendez (D-N.J.) said he had no intention of resigning during the trial phase of the corruption investigation against him. (Reuters)

“I’m angry and ready to fight,” Menendez, who is Cuban American, said to chants of “Viva Bob” in a Newark hotel.

Melgen was also indicted Wednesday. A grand jury in New Jersey issued eight counts each against Menendez and Melgen alleging bribery and three counts each alleging honest-services fraud, according to a statement from the Justice Department. They also each face one count of conspiracy and one count of violating the Travel Act. Menendez was also charged with one count of making false statements. Each of the eight bribery counts carries a maximum prison sentence of 15 years.

Justice Department officials had for weeks telegraphed their intention to indict the senator, and Menendez’s legal team has spent the past few weeks in a furious effort to persuade agency officials not to file charges.

Menendez, one of his party’s leading voices on international issues, restated his intention to stay in office during the trial phase of the case, which could last many months or years. “I am not going anywhere,” he said again Wednesday.

Later in the day, however, Menendez’s office announced that he would temporarily step aside as the top-ranking Democrat on the Senate Foreign Relations Committee while he battles the criminal case.

His Senate term does not end until early 2019, but if he is convicted and resigns or is expelled from the chamber, state law calls for the governor to make a temporary appointment and set a date for a special election. He is expected to appear in federal court Thursday to enter a not-guilty plea.

So far there is little pressure on Menendez to resign. Sen. Charles E. Schumer (D-N.Y.), who is expected to lead Senate Democrats after the 2016 elections, said in a statement that Menendez "is one of the best legislators in the Senate and is always fighting hard for the people of his state.”

“ I am confident he will continue to do so in the weeks and months ahead," Schumer said. 

The indictment, overseen by the Justice Department’s public-integrity unit in Washington, was approved by Attorney General Eric H. Holder Jr. and other top officials in the department. The 68-page charging document alleges a litany of previously undisclosed gifts that Menendez is alleged to have received and provided more details on the alleged favors that the senator’s office provided Melgen. Prosecutors also allege that Menendez helped three of Melgen’s foreign-born girlfriends obtain visas to visit the United States.

The gifts to Menendez included 19 free rides on private jets to resort locations, often with guests of the senator aboard; long weekends to visit Melgen in West Palm Beach, Fla., or his villa in an exclusive Dominican resort; and campaign donations, including $600,000 to a super PAC that spent heavily on the senator’s behalf during his 2012 reelection campaign.

The case against Menendez began under bizarre circumstances, even by the standards of politics in New Jersey, where public corruption has been a focus of the U.S. attorney’s office in Newark for several decades.

In 2012, during Menendez’s bid for a second full Senate term, an anonymous tipster using the pseudonym “Pete Williams” reached out to media outlets and to the FBI suggesting that Menendez was patronizing underage prostitutes on his Dominican vacations with Melgen. (Pete Williams is the name of the last New Jersey senator to be charged with corruption. Harrison “Pete” Williams was convicted and resigned in 1982 before the Senate expelled him. He died in 2001.)

The prostitution allegations fizzled, but investigators began scouring Menendez’s relationship with Melgen.

When investigators first began examining Menendez’s links to Melgen, the senator wrote a personal check for $58,000 to cover the cost of two private-jet flights that ferried Menendez to Melgen’s Dominican villa. His aides issued a statement at the time calling it an “oversight” and “sloppy” that those personal trips were not previously paid for, but there was no mention in the January 2013 statement of the other 17 private flights that Melgen allegedly paid for to fly Menendez, including nine trips in 2010 alone.

The charges against Menendez land as he is playing a high-profile role in two matters under fierce debate in the Senate.

One is the possible nuclear deal with Iran. First as chairman and now as ranking Democrat on the Foreign Relations Committee, Menendez has been the most prominent Democratic voice raising qualms about the ongoing multilateral negotiations. He is the lead Democratic sponsor of a bill — expected to move forward once the Senate returns April 13 — that would bring any Iran deal before Congress for a 60-day review.

Menendez could be pivotal in Loretta Lynch’s confirmation as attorney general, which has lingered for months. With scores of Republican senators saying they oppose Lynch’s confirmation because of her views supporting President Obama’s immigration policies, every Democratic vote — plus a potential tiebreaker from Vice President Biden — could be needed to secure a majority.

The indictment outlines a four-year bid to help Melgen, from 2009 through 2012, in his dispute with federal health agency officials. In early June 2012, Melgen issued a check for $300,00 for the Majority PAC, earmarked to help Menendez’s reelection. That same month, the senator went to bat for Melgen again, this time on behalf of his eye clinics, with top officials in the Department of Health and Human Services who oversaw Medicare reimbursements and whose auditors had concluded Melgen had overbilled the federal health program for eye medications he used in his clinic. Menendez, using talking points created by Melgen’s lobbyist, talked by phone on July 2 to the acting administrator at the Centers for Medicare and Medicaid Services about her agency’s policy for reimbursing physicians such as Melgen who used a single vial of medication multiple times, sometimes for multiple patients.

But the senator “expressed dissatisfaction” when the acting administrator told him the agency would not change its policy on reimbursements for this multi-dosing and warned that multiple uses of a single dose could increase the risk of infection.

The senator next had his staff arrange a meeting with then-HHS Secretary Kathleen Sebelius, which occurred in August 2012 at the behest of Sen. Harry M. Reid (D-Nev.), who was majority leader at the time.

Investigators also focused on Menendez’s help after the doctor became the chief investor in a company holding a long-dormant port-security contract in the Dominican Republic. The contract called for paying lucrative fees for security screening of ships coming into ports.

In April and May 2012, when Menendez reached out to top officials at the State Department to urge them to pressure the Dominican Republic’s government to enforce a port-security contract that will benefit Melgen’s company, Melgen was simultaneously e-mailing Menendez’s staff to promise he would deliver $60,000 in campaign donations, the indictment charges. Prosecutors allege Menendez met a State Department assistant secretary to discuss the security screening contract on or about May 16, 2012 — the day Melgen and his family donated $40,000 to the New Jersey Democratic State Victory campaign and $20,000 to Menendez’s legal defense fund.

That day, May 16, the assistant secretary wrote to his staff about the meeting and Menendez’s concerns about corrupt officials blocking the port contract in the Dominican Republic. The State Department official said he told the senator it was complicated.

“He said he wanted to hear of a solution by July 1,” he wrote. “If not, he would call a hearing to discuss it.”

In July, Menendez scheduled a Foreign Relations Committee hearing on U.S. companies doing business in Latin America.

During the hearing, he pressed the State Department to provide help to U.S. companies that were struggling with contracts in the Dominican Republic. Without naming Melgen, he mentioned an American company that owned part of a contract to do port security scanning.

Menendez called on State Department officials to “send a message that you cannot with impunity go ahead and violate those agreements.” He added: “If those countries can get away with that, they will. And that puts American companies at a tremendous disadvantage.”

Mike DeBonis and Rosalind S. Helderman contributed to this report.