If the extent of Menendez's missteps are two previously undisclosed flights he took on a plane owned by South Florida eye surgeon Salomon Melgen, the Democratic senator will likely escape with little long-term damage, political insiders, observers, and ethics experts said.
"A politician taking free trips on a plane and getting caught and has to pay it back? Tell me something I don't know yet," said Patrick Murray, head of the Monmouth University Polling Institute, characterizing the likely reaction of most New Jerseyans.
Despite the national attention now on the allegations around Menendez, seven political insiders, including Democrats and Republicans, along with two ethics experts, agreed with Murray. One critical point: Menendez has nearly six years before he is up for reelection.
But if more serious problems lurk - and news reports Friday hinted that Menendez's ties with Melgen may have blended into his work in the Senate - the fallout could threaten his chairmanship, if not his political career.
At the very least, it could also undercut his role as a key figure in the bipartisan push for immigration reform.
"Anytime you read the name of a senator in the same article with the word FBI, it's a big deal," said Meredith McGehee, policy director of the Campaign Legal Center, an independent ethics-watchdog group.
The scope and target of the FBI probe is unclear. The Miami Herald has reported that the raid of Melgen's offices Tuesday focused on potential Medicare fraud. Melgen is a prominent Menendez donor, but there has been no official indication that Menendez is a target of a criminal inquiry.
"Sen. Menendez has been targeted before by politically-motivated false allegations," said a statement from his office. "He will continue to maintain his focus on doing the job the people of New Jersey elected him to do."
Menendez has admitted that he did not report two flights on Melgen's private plane in 2010 and did not reimburse Melgen until a month ago, paying $58,500 for the two round-trips to the Dominican Republic.
Though unsubstantiated claims linking Menendez to prostitutes have garnered more headlines, the 2010 flights pose the most concrete ethics problem for him so far. The unreported flights could be an ethics violation or worse.
The top Republican on the Senate ethics panel said the committee was eyeing the news. But historically, the penalties that committee has imposed for a delayed reimbursement have been small.
More serious damage would occur, though, if additional unpaid-for trips emerge, or if evidence indicates that Menendez used his Senate position to improperly help Melgen, a charge that is explosive, but difficult to prove.
That's why eyebrows rose at Friday's reports saying Menendez had urged federal officials to intervene on Melgen's behalf in a business dispute in the Dominican Republic. His actions last year were reported by the Miami Herald and New York Times.
Another critical question centers on why Menendez did not report his flights sooner, said Rob Walker, former chief counsel and staff director for the Senate and House ethics committees.
If Menendez shows that he simply forgot, Walker said in an interview, the issue will be "a blip."
But if there was "some improper purpose for the trip, or it was linked to something like a request for official action ... if the facts show that there was some reason for Sen. Menendez to not want anyone to know about this trip, that's a much more serious story," said Walker, a Washington-based lawyer with the firm Wiley, Rein.
Knowingly and willfully choosing not to disclose such trips could be a felony, Walker said.
Menendez's office said Friday that the delay in repaying Melgen "was an oversight" rectified "as quickly as possible" after it was discovered.
Conservative websites have published stories alleging that Melgen flew Menendez to the Dominican Republic for trysts with prostitutes. Menendez has called those stories false.
"These are nameless, faceless, anonymous allegations," Menendez told television crews who questioned him Thursday night.
Earlier that day, as New Jersey's political class rode a train to Washington for a state Chamber of Commerce dinner, the aisles buzzed with chatter about Menendez. While saying he is not in trouble now, some passengers were already gaming out the possibilities. Thinking of broader implications for Democrats, they pointed ahead to Aug. 27: If Menendez were to resign by that date, his Senate seat could be filled in an election in November.
A resignation after that day, though, would help Republicans. Gov. Christie would get to appoint a replacement - presumably a fellow Republican - who would enjoy more than a year in office leading up to a 2014 election. In the closely divided Senate, Democrats can hardly afford to lose Menendez's seat.
All of which, of course, is nothing but talk: Menendez has not been charged with anything unethical, much less unlawful. New Jersey's history sets a high bar for scandals, too, and it would take a lot to pry the strong-willed senator out of office.
He has survived scrutiny before, cruising to victory in his 2006 Senate run even amid a federal inquiry into his financial arrangement with a nonprofit. He was never charged.
And even a congressional ethics finding does not necessarily unseat its subject. David Vitter (R., La.) remains in the Senate after being linked to high-end prostitutes. Rep. Charles B. Rangel (D., N.Y.) won reelection after being admonished by a House ethics panel.
But New Jerseyans have seen plenty of public officials fall to scandal, including a recent Democratic senator. Robert Torricelli was forced to drop a reelection bid in 2002 after taking lavish gifts from a donor.
There are key differences. The controversy surrounding Torricelli peaked just months before he faced reelection. A grand jury was involved, and the Senate "severely admonished" him. When Democrats realized he could not win - and might drag down others on the ticket - they walked away, leaving him no buffer from crushing political and media pressure.
Menendez is nowhere near that point. No authorities have accused him of anything. Democrats have stood by him.
His political future may depend on whether any more news will test that loyalty, or if the initial furor soon dies down.
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