U.S. Sen. Robert Menendez of New Jersey pleaded not guilty to federal corruption charges in Newark court Thursday, a day after he was indicted on bribery and conspiracy offenses in connection with an ongoing investigation into his business dealings with a Florida doctor.

Menendez, a Democrat who has held his seat since 2006, was charged in a 14-count indictment Wednesday with accepting nearly $1 million in gifts and campaign contributions from Salomon Melgen, a longtime friend and wealthy Florida optometrist, in exchange for a stream of political favors. Melgen, also named in the indictment, pleaded not guilty Thursday as well.

Prosecutors allege he gave Menendez vacations, airline travel and tens of thousands of dollars in contributions to a legal defense fund. Melgen was also seeking Menendez's support of the visa applications of several of Melgen's girlfriends, according to the indictment.

According to the U.S. Department of Justice, Menendez lobbied on behalf Melgen's interests all the way up to the highest levels of U.S. government, meeting with a U.S. cabinet secretary, contacting a U.S. ambassador, meeting with other senior agency officials and executives, and soliciting other U.S. senators. He and Melgen had been under investigation for months.

Menendez's attorney, Abbe Lowell, entered the not guilty plea on his behalf less than 12 hours after Menendez promised to be vindicated and declared that he's "not going anywhere." The Democrat has temporarily ceded his leadership role on the Senate Foreign Relations Committee, however.

In court Thursday, Lowell echoed Menendez's comments from the previous evening, and said prosecutors at the Justice Department "often get it wrong."

Lowell compared the case to the government's failed prosecutions of former Alaska Sen. Ted Stevens and former North Carolina Sen. John Edwards. Stevens, R-Alaska, 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.

Edwards, D-North Carolina, was charged with campaign contribution violations in 2011, but was found not guilty on one count and a mistrial was declared on five others.

Menendez has acknowledged that he flew multiple times on Melgen's private jet to the Dominican Republic and initially failed to properly pay for the trips. Menendez in 2013 agreed to reimburse Melgen $58,500 for the full cost of two flights.

The senator's office later disclosed another flight, from Florida to New Jersey in 2011, and said Menendez had repaid Melgen $11,250 for it.

Last year, Menendez disclosed that his campaign accounts had paid a law firm $250,000 for legal costs related to investigations by the Justice Department and the Senate Ethics Committee of his ties to Melgen.

Menendez has also 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 that he and Melgen have been friends for decades.

At the news conference Wednesday, Menendez said, "I'm angry because prosecutors at the Justice Department don't know the difference between friendship and corruption, and have chosen to twist my duties as a senator and my friendship into something that is improper. They are dead wrong and I am confident they will be proven so."

Melgen came under renewed scrutiny when government data last year showed he had received more in Medicare reimbursements in 2012 than any other doctor in the country. He was released following Thursday's court hearing after posting $1.5 million bond. Menendez was released on his own recognizance; a judge ordered the senator to surrender his personal passport, but he can still travel on official Senate business. Trials for both men are tentatively expected to start in mid-July.

Lowell tried to argue that Menendez should be given special consideration because of his position. "He's not any other defendant," he said.

Menendez said in a brief statement to reporters that after a three-year investigation, he looks forward to responding to the allegations on the record in court.

"These allegations are false, and I am confident they will be proven false in court," Menendez said.

Melgen and his attorney left the courthouse without comment.

Menendez joined the Senate after serving more than a decade in the House of Representatives. A lawyer and former mayor of Union City, he also served in the New Jersey General Assembly and state Senate.

Even while under federal investigation, he used his leadership position on the Senate Foreign Relations Committee to criticize negotiations between President Obama's administration and Iran on its nuclear program and has been outspoken in opposition to normalizing relations with Cuba.
New Jersey's junior U.S. Sen. Cory Booker (D-NJ) expressed support for Menendez in a statement Wednesday, calling him an "invaluable resource and a mentor" since he arrived in the Senate.

"I won't waver in my commitment to stand alongside my senior Senator to serve our great state," he said.

The indictment comes as the confirmation of Loretta Lynch, the U.S. Attorney for the Eastern District of New York nominated by Obama as U.S. Attorney General, hangs in the balance.

A spokeswoman for Menendez said Thursday the indicted senator plans to vote in favor of her confirmation, securing the key vote Washington insiders had told NBC 4 New York would be needed to get Lynch the 50 she needs to be confirmed.