Sen. Bob Menendez, Democratic senator from New Jersey, appeared in the 2007 documentary “Last Best Chance.” The documentary is a part of a 12-part series about the immigration debate on Capitol Hill and across the country. (“Last Best Chance” produced by Epidavros Project Inc. and filmmakers Shari Robertson and Michael Camerini/How Democracy Works Now)

The intimate gathering stretched late into the night. Cigars and champagne toasts, a “picadera” of Dominican appetizers — only the finest at the well-appointed Caribbean retreat of the rich American doctor.

Some of the moneyed attendees slipped into stylish guayaberas for the evening, but the guest of honor, Sen. Robert Menendez, stuck to a stodgy blue blazer with a pin on the lapel. The New Jersey Democrat posed stiffly beneath a huge cubist-style painting. He was the center of attention but still somehow out of place among the guests invited by his traveling buddy, the Palm Beach ophthalmology mogul Salomon Melgen.

His friendship with Melgen, which has become the focus of a federal investigation, had brought him behind the gates of the ultra-exclusive Casa de Campo resort for an evening with heady company — Dominican elites, American entrepreneurs and international business executives. He was with them on that spring evening in 2010. But he wasn’t really of them.

Menendez, 59, had grown up without money and forged a career in the rough-edged landscape of New Jersey machine politics rather than the refined elegance of high society. He needed the rich as much — maybe more — than they needed him.

“Bob is probably one of the poorest guys in the Senate,” said Rep. Albio Sires (D-N.J.), his longtime friend and confidant. “He has to scrap and scrape and claw and talk to people to try to raise that money. . . . It makes you vulnerable to something going on.”

Now Menendez’s relationship with one of his wealthy patrons has drawn the scrutiny of the Senate Ethics Committee and a federal grand jury in Miami, which, according to three people familiar with the investigation, is examining his role in advocating for Melgen’s business interests.

Until Menendez’s relations with Melgen drew the attention of investigators, the senator’s influence in Washington had been growing.

He had proved his bona fides as a fundraising powerhouse for Senate Democrats and a hero to Hispanic activists. He ascended last month to the coveted chairmanship of the Senate Foreign Relations Committee and emerged as a prominent player in one of the year’s biggest legislative battles when he joined bipartisan talks over a possible landmark law to remake the U.S. immigration system.

Melgen, toasting Menendez at the May 2010 reception at Casa de Campo, praised the senator as “not only the leader of Hispanic Americans in the United States but the leader of Hispanics in the Americas,” according to a local society column reporting on the event.

Melgen has been a prolific campaign donor, giving more than $700,000 to Menendez and other Senate Democrats ahead of last year’s election. He has also provided the senator with free flights on his private jet and hospitality at his Dominican vacation home, according to people familiar with their relationship. Menendez has sought to apply pressure on the Dominican government to enforce a contract with Melgen’s port security company and has interceded with federal health-care officials after they said Melgen had overbilled the federal Medicare program for treatment at his eye clinic.

Menendez has said his efforts involving the port security deal and the Medicare payments were proper. But he has acknowledged failing to disclose two trips provided by Melgen in 2010, as required by Senate rules. In January, he wrote a personal check for $58,500 to reimburse his friend. The sum represented a substantial burden for Menendez, coming to between 33 percent and 87 percent of all the money he has in bank accounts and stocks listed on his most recent Senate disclosure statement, which gives amounts in broad ranges.

In an interview Thursday in his Senate office, Menendez waved off any concerns about a federal investigation, saying any review would find he “acted appropriately at all times.” Still, he said, collecting campaign dollars can be an uncomfortable practice.

“For me, raising money to fund a campaign is contrary to what I learned growing up in life, which is you work for everything and you ask for nothing,” he said, noting that he has for years supported public financing of campaigns and other changes to let lawmakers focus on their work. “But that’s a reality for anybody who runs for office who isn’t personally wealthy.”

Several people close to Menendez said in recent days the controversy has taken a toll on the senator, though in public he appears confident and remains engaged with his job.

Some Menendez allies have begun to worry about whether his closeness to Melgen could expose him to legal problems or, at a minimum, jeopardize his legacy. Could much of Menendez’s success now be tainted by the very culture of dealmaking, relationship-building and aggressive fundraising that he mastered over so many years?

The loyal grinder

Menendez, raised in a Union City tenement by Cuban immigrant parents, represents an unusual breed of politician in the Senate. He does not hail from a dynasty or wealth, nor is he a celebrity in the mold of President Obama or Sen. Marco Rubio (R-Fla.). He is, instead, a grinder.

His father was a carpenter with a terrible gambling problem who committed suicide when Menendez was in his early 20s. His mother was a seamstress. Menendez was the youngest of three siblings and, as the only one born in the United States, singled out by his family to succeed.

He started in politics at age 19 with a petition drive to reform the local school board. His motive was personal — anger over having been told as a high school student that he couldn’t join the honors program if he couldn’t afford to pay for the books himself.

By the time Menendez was 27, he was steeped in the seamy politics of North Jersey. Facing death threats, he donned a bulletproof vest to testify against a mentor, Union City Mayor William Musto, who was convicted of racketeering for funneling education dollars to mobsters.

Menendez went on to be elected mayor of Union City and then as an assemblyman in the state legislature. Associates say he engendered fear more than affection. He recognized supporters by helping them land jobs or make connections while feuding with local political rivals over spending public money or recruiting party candidates, according to people who knew Menendez at the time.

“Bob is very loyal to people who help him — I’ll put it that way,” Sires said. “He always remembers who’s on his side.”

Menendez helped transform the legendary Hudson County political machine, tapping the fast-growing Hispanic population to depose the Irish and Italian immigrants around Jersey City who long dominated Democratic politics. He developed close ties with the local anti-Fidel Castro Cuban exile community.

A newly drawn, heavily Hispanic congressional district elected him to the U.S. House in 1992. When he achieved his lifelong aspiration of becoming a U.S. senator in 2006, appointed to the job by Gov. Jon Corzine to fill the seat Corzine had just vacated, many Menendez allies hoped he had finally transcended the grittier aspects of his hometown politics.

But as a senator from New Jersey, where running statewide requires expensive advertising in the New York and Philadelphia media markets, the pressure to raise campaign money was intense. Menendez kept a firm grip on the New Jersey Democratic Party apparatus, a key tool for bringing in donations.

As Menendez campaigned to keep his Senate seat in 2006, prosecutors working for then-U.S. Attorney Chris Christie launched a grand jury probe into whether the senator improperly helped steer federal funds to an anti-poverty group that had rented a modest brick house he owned in Union City. Investigators also looked at whether he had helped a fledgling lobbying firm started by his former chief of staff. Menendez denied wrongdoing, and allies accused Christie, a Republican who later would become governor, of waging a partisan investigation.

The five-year probe officially ended in October 2011 with no charges filed, but it invited political attacks from Republicans.

Now there is another grand jury looking into a Menendez relationship. And friends say Menendez is angered that the Melgen controversy, no matter the outcome of the current federal probe, threatens to reopen all those old wounds. One friend likened the senator’s frustrations to that of the fictional Michael Corleone, who famously complained of his ­organized-crime family in the “Godfather” movies that “just when I thought I was out, they pull me back in.”

“How long does he have to be the guy from Hudson County?” asked Menendez’s friend, speaking on the condition of anonymity to describe the senator’s feelings.

A symbol for Hispanics

As Menendez gained influence in Congress, he emerged as a symbol of rising Hispanic power.

He became a regular guest on Spanish-language media and traveled the country recruiting new Hispanic candidates and finding new Hispanic donors.

He was a Cuban American with hard-line views on retaining tough sanctions on Cuba’s Communist regime, a stance that put him in good stead with the traditionally Republican Cuban exiles of South Florida.

But his down-the-line liberal views on civil rights and immigration helped him broaden his reach into non-Cuban Hispanic communities from Texas to California. He forged ties with non-Hispanic colleagues in Congress by counseling them on how to understand the growing immigrant communities in their districts.

His leadership role in the U.S. House, where he rose to his party’s No. 3 position, and as chairman of the Democratic Senatorial Campaign Committee in 2010 came before the national political parties began showcasing new Hispanic stars. His rise, he wrote in his 2009 book, “Growing American Roots , showed that “people like me were just plain qualified for the job.”

“He is the most powerful Hispanic politician in America and certainly the most successful Hispanic in the U.S. Congress,” said Rep. Joe Garcia (D-Fla.), a Menendez ally and fellow Cuban American. “But he’s powerful because he’s a great politician, not because he’s Hispanic.”

Yet Menendez has not been promoted by party strategists as a prominent figure to rally Hispanic voters. Nor has he been fully accepted by many Democratic colleagues, some of whom quietly dismissed his ascent to head the Foreign Relations Committee as the result of more senior senators’ choosing other posts outside the panel.

His frosty relations with Obama are widely known in Democratic circles, left over from his strong support of Hillary Rodham Clinton in the 2008 primaries. Last year, wary of the senator’s history, Obama’s team looked past Menendez to land a Hispanic keynote speaker for the Democrats’ national convention, opting for the little-known mayor of San Antonio, Julian Castro.

Menendez’s brusque style has strained his relations even with close allies. At a tense meeting with some of the country’s leading immigration activists in 2007, for instance, he accused them of being a “punching bag” for conservatives who were pushing to impose strict limits on the rights of citizens and legal immigrants to bring close family members into the United States.

“I have to say, I’m disappointed in all of you,” he told a gathering of grim-faced activists, who were seated on couches and standing around his Senate office.

When one of the advocates, Karen Narasaki, tried to dispel the awkwardness by thanking Menendez for his work, he cut her off. “Please, let’s save the thank-yous. I really don’t want to hear them,” he said as Narasaki began to cry. Menendez handed her a tissue. The exchange was caught on video by a crew filming for a documentary, “Last Best Chance,” about the failed immigration overhaul efforts of 2007.

Still, Narasaki said later, she views Menendez as a “knight in shining armor” of the immigrant rights movement. And other advocates see the senator’s stubbornness as part of what makes him an effective protector of their interests in the current bipartisan talks. “He is our champion,” said Janet Murguia, president of the National Council of La Raza. “People admire his personal story and the fact that he’s never forgotten his roots.”

Menendez and Melgen

Melgen, too, was drawn to Menendez. The two met shortly after Menendez was elected to Congress, and Melgen was attracted by his friend’s stature as a powerful Hispanic politician and by their shared interest in advancing Hispanic causes, said several people familiar with the relationship.

The two men are in many ways an odd pairing. Melgen, 58, is a gregarious personality quick to giggle. He has expensive tastes and is often seen surrounded by beautiful women.

Menendez is cerebral, some say Yoda-like. Divorced in 2005 and the father of two grown children, he lives a spartan lifestyle, keeping a small apartment in a working-class North Bergen, N.J., neighborhood and another on Capitol Hill. He is often seen eating breakfast at a Union City IHOP, alone or with staff, always ordering three eggs over easy, corned-beef hash and dry rye toast. He often refers to his home town to demonstrate how he, unlike most senators, can relate to the struggles of everyday Americans.

“It gives me a perspective of what the average person faces,” he said. “I still live largely on my salary.”

Yet the senator and the eye doctor have grown close and enjoy each other’s company, associates say. Melgen, a Dominican-born immigrant, sees the U.S.-born Menendez as the embodiment of American success and an important player on the national stage, and frequently refers to him as a “great man,” associates say. “Sal is sort of flattered to be with Menendez,” one person said.

Melgen’s attorney has said the doctor, proud of the friendship, is not worried about any investigation into the relationship. Moreover, the lawyer said, Melgen’s firm has a legal contract to provide port security that the Dominican government should enforce, and he said Melgen’s Medicare billing was justified.

Menendez speaks in adoring terms about Melgen and his wife. “We’ve developed a close relationship together,” he said, describing Melgen as “a very thoughtful guy.”

The two have spoken weekly over the past 20 years. Menendez has visited Melgen at his Dominican home more than two dozen times, according to a person familiar with their relationship.

In the interview Thursday, Menendez rejected the notion that his relationship with Melgen was problematic. Melgen’s requests often aligned with Menendez’s public policy aims, the senator said. Menendez pointed to his efforts on behalf of Melgen’s port security deal in the Dominican Republic, which called for operating X-ray scanners to screen cargo. This fit with the goal of fighting drugs and terrorism, the senator said.

Menendez’s friends and supporters often raise policy issues in social settings. And while he said he would usually prefer to be talking about sports or music rather than his work in Washington, the discussions “inevitably head in that direction.”

“It’s like the family member who’s a doctor and everybody starts asking them, ‘Oh, I have this twitch, I have this pain,’ or the family member who’s a stockbroker and [says], ‘Hey, you got any good tips for me?’ ” Menendez said.

Addressing a predominantly African American church in Trenton recently, Menendez laid out for congregants the milestones of his unlikely rise from poverty, vowing to battle on. “I have worked too hard and too long in the vineyards to allow my hands full of harvest to be soured,” he thundered from the pulpit.

Rep. Sires feels confident that his old friend will survive politically. Yet, still he worries. “He was very careful, never careless,” Sires said. Then again, he said, “you can only be so careful.”

Alice R. Crites and Julie Tate contributed to this report.

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