WASHINGTON - Sen. Robert Menendez is prepared for a long fight.

The New Jersey Democrat has hired two lawyers and a crisis consultant and has gone about his business as newly named chairman of the Senate Foreign Relations Committee even as federal investigators probe his ties to a top campaign donor and editorials in his home-state newspapers call for him to step down.

"He's worked hard, and he's focused," says a rising Republican star on the committee, Florida Sen. Marco Rubio.

The most salacious allegations facing Menendez, involving trysts with prostitutes in the Dominican Republic, have been discredited.

The most substantial questions, centered on Menendez's lobbying on behalf of friend and donor Salomon Melgen, have emerged in a slow drip of news stories and are the subject of several investigations, including, according to the Washington Post, a Miami grand jury.

Each of those investigations, though, is secretive and slow-moving. A more immediate public concern for Menendez could be political pressure.

So far, there's been little.

A Senate Democratic leadership aide said last week there had been zero talk of removing Menendez as chairman of the Foreign Relations Committee, an influential post he assumed in late January, just before the spate of critical accusations gained steam. A second Democratic aide, not tied to Menendez, also said there was no pressure mounting within the caucus to oust him and move him out of the spotlight.

The New York Times, Newark Star-Ledger, and Asbury Park Press editorial boards have all called for Menendez to step aside as Foreign Relations Chairman. But Democrats, including Senate Majority Leader Harry Reid of Nevada, have stood by him, and Republicans have taken a pass on the allegations.

"Nothing has stopped me from pursuing the committee's interests and agenda," Menendez said Wednesday in an Inquirer interview after leading a Foreign Relations hearing on U.S. counterterrorism. "My colleagues both on and off the committee are supportive."

Some of the media heat has come off the story now that the prostitution claims, first published by the conservative website the Daily Caller, have been discredited. Accusers, according to Dominican authorities, have admitted to being paid to make up accusations.

But federal agents, reporters, and independent groups are still scrutinizing Menendez's record, and ethics watchdogs said concerns about whether he improperly used his office to aid Melgen must be addressed.

"The other [allegations] were far more serious than the prostitution thing from the get-go," said Melanie Sloan, executive director of Citizens for Responsibility and Ethics in Washington, a nonpartisan watchdog group. "The questions about what he has done for Dr. Melgen, what he may have received in exchange, those are serious questions."

Menendez has admitted that he twice flew on Melgen's private plane to the Dominican Republic and that he did not repay the $58,500 cost for more than two years. He has said the delay was an oversight.

He also lobbied federal officials on Melgen's behalf in disputes involving a Medicare billing dispute and business deal in the Dominican Republic, according to news reports. Other stories delved into instances of Menendez's helping other donors, though he has said he acted properly.

A slow build is common in political scandals, noted Ken Boehm, chairman of the National Legal and Policy Center, a right-leaning watchdog group that helped bring to light records of Menendez's speaking up for a Melgen business interest at a hearing.

"The model is, this will take some time," Boehm said.

An adviser close to Menendez who spoke on condition of anonymity countered that the story may already be waning, citing the muted public reaction to some of the latest revelations.

Republicans have been cautious, other than using Menendez as the butt of partisan jokes.

The Republican congressional campaign arm has included Menendez in a basketball-style "Liberal Madness" tournament bracket on its website. Menendez was the No. 2 seed in the "Backroom Dealers" region. (He lost in the second round to liberal financier George Soros).

Republicans on the Foreign Relations Committee - such as Rubio, who is working with Menendez as part of a group of senators crafting a bipartisan immigration-reform plan, have repeatedly declined to comment.

"I respect Sen. Menendez and the position that he's in," said Sen. John McCain (R., Ariz.), another committee member.

Menendez, a survivor of previous inquiries, has hired crisis consultant Matt Miller, a former campaign aide and spokesman for Attorney General Eric Holder; and two Washington lawyers: Marc Elias, chair of the political law practice at Perkins Coie; and Stephen Ryan, head of the government strategies group at McDermott, Will & Emery.

If his colleagues in the Capitol have demurred, his critics back home have not. Last week began with New Jersey's largest newspaper, the Star-Ledger, calling for him to relinquish his seat as Foreign Relations chair.

Menendez proceeded as normal. He sent out news releases on the Persian new year and Greek Independence Day, and led his hearing Wednesday. Unlike the early days of the furor, only one reporter waited in the hall until the hearing ended.

Such are the rapid twists of this story.

Though Menendez appears to have some political breathing room, long-term legal questions remain.

The Senate Ethics Committee is looking into his actions, though that panel can take years to act.

And then there is the grand jury, though its involvement does not necessarily signal an escalation, said two former corruption prosecutors and a former federal investigator.

Grand juries provide the power to subpoena documents and witnesses, steps any prosecutor could take as standard operating procedure in such a high-profile case, said lawyer Rob Walker, formerly of the Department of Justice's public integrity unit.

Especially in light of the added public scrutiny the case has attracted, he said, "You want to make sure that you get everything right - and to get it right, you want to use, as a prosecutor, all the tools at your disposal, and the most powerful tool is the subpoena."

The FBI raided Melgen's medical offices in late January, reportedly as part of an investigation into potential Medicare fraud, but prosecutors will examine every angle, regardless of how likely charges are, Walker said.

Jay Fahy, who once led the special prosecutions unit in New Jersey's U.S. Attorney's Office, agreed.

All three former federal law enforcement officials said it would be difficult to bring criminal charges based only on Menendez's actions and Melgen's donations.

"I can't see it as a case with any legs," Fahy said.

With any quid pro quo, Walker said, "you're going to have show a real agreement, and it's just very hard to do that."

Menendez's failure to report his two trips on Melgen's plane could be a felony if it is shown that the senator intentionally omitted the information, Walker said. But he and the other two former officials said prosecutors were unlikely to build a case on that issue alone.

As for the grand jury, and any shadow the federal investigation may cast over Menendez's interaction with foreign leaders, the senator told a reporter after Wednesday's committee hearing: "Only you all are interested in that."

Contact Jonathan Tamari at jtamari@phillynews.com or follow on Twitter @JonathanTamari. Read his blog, "Capitol Inq," at www.philly.com/CapitolInq.