NEWARK, N.J. - Sen. Robert Menendez (D., N.J.) foreshadowed the argument he hopes will save his career as he began his formal fight against corruption charges Thursday.

Menendez and South Florida eye doctor Salomon Melgen, a longtime friend and major donor, each pleaded not guilty to charges that Melgen won the senator's support with lavish gifts described in vivid detail over a 68-page indictment.

"Prosecutors get to write the indictment they want, after a secret, one-sided presentation in a grand jury," Menendez attorney Abbe Lowell said after the afternoon hearing. "Now they have to make good on those charges. Now they have to prove beyond a reasonable doubt that a 20-year friendship between Sen. Menendez and Dr. Melgen was something else."

The statement touched on the crux of Menendez's defense against 14 counts of conspiracy, bribery, and other charges: that the gifts from Melgen were presents to a friend, not bribes.

When the charges were announced Wednesday, Menendez said prosecutors "don't know the difference between friendship and corruption."

Lowell, citing botched federal prosecutions against the late Sen. Ted Stevens (R., Alaska) and former presidential candidate John Edwards, called the charges against Menendez "the latest mistakes."

But former prosecutors were impressed by the level of detail in the indictment alleging that Melgen's generosity went beyond friendship and led to official help.

"The Stevens indictment was relatively thin," said one, Robert Walker. "This one's a phone book."

It describes Melgen's providing a stay at a five-star Paris hotel, more than a dozen private flights for Menendez or his guests, car service and more, and Menendez's using his office to apply pressure to help his friend's business and personal interests.

Though there is no record of Menendez promising anything in exchange for Melgen's generosity, Walker, a former attorney in the Justice Department's public integrity section, said the narrative seems aimed at painting a broad, comprehensive picture of the senator's allegedly helping his donor far more than an average constituent.

"Yeah, you exchanged gifts: He gave you this, and you gave him official action," said Walker, now an attorney at Wiley Rein, characterizing the charges. "That's what the prosecution is aiming at and driving at."

Walter Timpone, who once led the public corruption unit in the U.S. Attorney's Office in New Jersey, said, "Friendship has to steer clear of ethical lapses, and I think that's again where the battle is going."

On its face, the friendship argument is plausible, said Andrew Levchuk, a former attorney in the public integrity section.

"The question is, how active was the senator on behalf of his friend?" said Levchuk, now a defense attorney at the firm Bulkely Richardson in Massachusetts. "Were these things that Melgen, given his friendship, would have done for Menendez anyway? Or in fact, did he keep the gravy train flowing so he could continue to get favors?"

Menendez's lawyers plan to chip away at the many details laid out in the indictment, aiming to have some elements thrown out and diminishing the case prosecutors have presented.

Lowell - who also defended Edwards - "is a wonderful defense lawyer who could basically poke holes through a steel door," Timpone said.

Some of Menendez's actions in the indictment, the senator plans to argue, are protected by the Constitution's "speech or debate" clause, which shields lawmakers from prosecution for legislative activity, according to a Menendez ally. The ally insisted on anonymity to discuss Menendez's legal strategy.

The senator's many stays at Melgen's luxurious Dominican Republic villa are allowed under Senate rules permitting stays at a friend's home, he plans to argue.

And more than $700,000 in campaign contributions detailed from Melgen to Menendez are allowed under federal rules, his legal team plans to say.

"What they will try to do is limit the evidence that comes in," Levchuk said. "They don't have to knock out everything ... but if you can limit the number of quid pro quo items, if you will," it can weaken the government's case.

Each of Menendez's arguments, of course, will likely be contested by prosecutors.

And he does not have easy answers for several issues in the indictment.

The ethics exception for staying at a friend's home won't apply to the three-night stay in Paris, valued at close to $5,000, that Melgen paid for with American Express points.

Menendez's meeting with a cabinet official, where he pushed Melgen's argument in an $8.9 million Medicare billing fight, likely won't fall under the speech or debate clause.

And the senator failed to disclose the vast majority of the flights he took on Melgen's jet, many of which had not been reported until the indictment was released.

That omission may help prosecutors argue that Menendez had criminal intent, Levchuk said. If the flights were OK all along, they can ask, why didn't he report them?

Menendez remained defiant Thursday.

"These allegations are false, and I am confident they will be proven false," he told reporters outside the federal courthouse.

After the hearing, Menendez, 61, was released on his own recognizance and was required to surrender his personal passport, but not his official one.

Melgen, 61, of West Palm Beach, was released on $1.5 million bail. He was ordered to remove all firearms - many in his son's collection - from his South Florida home, and surrendered his U.S. and Dominican passports. He will lose access to his private jet.

Menendez and Melgen smiled at each other before the hearing. Neither spoke during the brief proceeding before U.S. District Judge William H. Walls.

Menendez is next scheduled to appear in court April 22 for a procedural matter, and a tentative trial date was set for summer.

Afterward, Lowell called on prosecutors to investigate leaks to the press concerning the case.

Menendez, meanwhile, continued to weigh in on the issues of the day, including the international agreement on Iran's nuclear program - a cause the senator has watched closely.

The deal was announced during his court hearing, but Menendez, who has temporarily stepped down as the top Democrat on the Senate Foreign Relations Committee, still blasted out a statement.

Later, another release shared his thoughts on World Autism Day.