U.S. Senator Bob Menendez (D-NJ) arrives to the Federal court in Newark, New Jersey April 2, 2015. Senator Menendez of New Jersey was indicted on corruption charges, allegations that the high-ranking Democrat vowed to fight at a news conference on Wednesday night. [Photo/Agencies]

NEWARK, New Jersey - Prominent Democratic Sen. Bob Menendez pleaded not guilty Thursday to charges that he accepted nearly $1 million in gifts and campaign contributions from a longtime friend in exchange for a stream of political favors.

An attorney for Menendez entered the plea before a federal judge in Newark, one day after he promised to be vindicated and declared that he's "not going anywhere."

The criminal charges brought cloud the political future of the top Democrat _ and former chairman _ of the Senate Foreign Relations Committee, who has played a leading role in Congress on matters involving Iran's nuclear program and U.S. efforts to improve ties with Cuba.

The indictment alleges Menendez used the power of his Senate seat to benefit Salomon Melgen, a wealthy Florida eye doctor who prosecutors say provided the senator with luxury vacations, airline travel, golf trips and tens of thousands of dollars in contributions to a legal defense fund.

Melgen also entered a not guilty plea, and Judge William Walls set a tentative July 13 trial date. He remains free but had to surrender his passport.

The investigation that led to the indictment came into public view when federal authorities raided Melgen's medical offices in 2013. It will almost certainly lead to a drawn-out legal fight between Menendez and a team of Justice Department prosecutors who have spent years investigating his ties to Melgen.

It will require prosecutors to prove that a close and longtime friendship between the men was used for criminal purposes, and it is likely to revive the legal debate about the constitutional protections afforded to members of Congress for acts they take in office, which Menendez has already signaled as a possible line of defense.

Menendez said he would temporarily step aside from his role as top Democrat on the Foreign Relations Committee but appeared more defiant than ever at a news conference Wednesday.

"I am not going anywhere. I'm angry and ready to fight because today contradicts my public service and my entire life," Menendez told reporters.

Menendez's lawyer, Abbe Lowell, compared the case to the government's bungled prosecution of former Alaska Sen. Ted Stevens, a Republican who was indicted in 2008 on charges of not reporting hundreds of thousands of dollars' worth of home renovations. Stevens was found guilty but the Justice Department later dismissed the case and said prosecutors withheld evidence that would have been favorable to the defense.

"Prosecutors in the Justice Department often get it wrong," Lowell told reporters Thursday after the brief hearing. "These charges are the latest instance of that."

The indictment from a grand jury in Newark contains 14 counts _ including bribery, conspiracy and false statements _ against Menendez and charges Melgen, a political donor to Menendez and other Democrats. Menendez had already acknowledged that he had taken several round-trip flights to the Dominican Republic on Melgen's luxury jet that, initially, were not properly reimbursed. But the document spells out many additional gifts, such as a Paris hotel stay and access to a Dominican resort, that prosecutors say were never reported on financial disclosure forms.

In exchange for those and other gifts, prosecutors allege, Menendez sought to smooth approval of the visa application process for several of Melgen's foreign girlfriends, worked to protect a lucrative contract Melgen held to provide cargo screening services to the Dominican Republic and intervened in a Medicare billing dispute on the doctor's behalf worth millions of dollars.

In 2013, in an email exchange one day after Melgen and Menendez had golfed together in Florida, Menendez told a staffer to contact U.S. Customs and Border Protection to stop them from donating shipping container monitoring and surveillance equipment to the Dominican Republic, according to the indictment. Melgen had a contract to provide exclusive cargo screening services in Dominican ports, and the Customs and Border Protection plan would have hurt his financial interests, prosecutors say.

Menendez has acknowledged taking actions that could benefit Melgen, among them contacting U.S. health agencies to ask about billing practices and policies. But the lawmaker has said he did nothing wrong and the interactions he had with the doctor were reflections of a close friendship dating two decades.