Washington (CNN)Sen. Robert Menendez might be a senior Democrat but he's no friend of the White House.
Menendez: White House's least favorite Dem
In fact, he's emerged as one of the most troublesome obstacles to President Barack Obama's legacy-building effort to end decades of U.S. estrangement with Cuba and Iran. He's also poked the administration on its troubled relationship with Israeli Prime Minister Benjamin Netanyahu, with whom he shares a hawkish outlook towards Tehran.
But the senior senator from New Jersey, 61, is now in the news for a different reason, after CNN first reported Friday that the Justice Department is preparing to bring criminal charges against him.
People briefed on the case say prosecutors plan to allege that Menendez used his Senate office to push the business interests of a Democratic donor and friend in exchange for gifts. The charges, which are expected to be formally laid within weeks, threaten to seriously imperil Menendez's political prospects at a time when his influence in Washington has rarely been greater.
Menendez is currently the ranking Democrat on the Senate Foreign Relations Committee, after serving briefly as chairman when his predecessor John Kerry left to become Secretary of State and before Democrats lost the Senate majority last year.
But his position in the minority belies his influence.
Menendez has joined Republicans to threaten Obama's top-second term foreign policy priority, a nuclear deal with Iran. He is currently crucial to the administration, despite his distance from the White House, as some Democrats are likely to take his lead as they consider how to respond in the event an agreement is reached.
Politically, Menendez, who fashioned his rise to the powerful post at Foreign Relations slowly, deliberately and largely out of the public spotlight, might be the antithesis of Obama, who appeared almost from nowhere and rocketed to the pinnacle of U.S. politics.
But he is respected on Capitol Hill for making it to the top after years of striving, serving as mayor of his home town and in the New Jersey state assembly before winning election to the House of Representatives in 1992. He masterminded the Senate Democratic election campaign in 2010 in which the party clung onto the chamber despite stiff political headwinds that erased the party's grip on the House.
It is unclear whether the charges being prepared against Menendez will lead to political pressure that could throw his position on the Foreign Relations committee into question. He is not up for re-election until 2018. His spokeswoman, Tricia Enright, said that all of Menendez's actions were "appropriate and lawful and the facts will ultimately confirm that."
Lately, Menendez has taken to wearing his testy relations with the Obama administration as a badge of honor.
"I don't get calls from the White House," Menendez was quoted by the New York Times as telling reporters this week.
He was also a strong supporter of Netanyahu's speech to Congress on Tuesday which was critical of the Iran nuclear deal. Menendez took a direct shot at the administration's fervent opposition to the event.
"I take issue with those who say the prime minister's visit to the United States is 'destructive to U.S.-Israel relations,'" Menendez said at the American Israel Public Affairs Committee annual conference, referring to comments by National Security Advisor Susan Rice.
White House officials privately do not try to hide their disappointment with Menendez. Some have previously complained that his approach to foreign policy is not distilled from the wide sweep of American global interests but is the product of domestic political motivations.
Obama aides with long memories also have not forgotten that he was an early supporter of Hillary Clinton against Obama in their 2008 clash for the Democratic nomination.
The Senator does, however, share the White House's enthusiasm for comprehensive immigration reform which has yet to make it through Congress.
The place where Menendez grew up, Union City, New Jersey, has the highest number of Cuban exiles in the United States outside Miami and the senator has been a frequent and reliable scourge of Fidel Castro and his successor as Cuban leader, Raul Castro.
The son of Cuban immigrants, Menendez fiercely opposed the Obama administration's effort to engage Cuba, accusing the White House of handing its government an economic lifeline at a time when its support from Venezuela was drying up because of low oil prices.
"I think it stinks," said Menendez in a press conference in December of the deal.
"I think it's wrong. I am deeply disappointed in the president," he said, according to NJ.com.
Last month, Menendez complained to CNN that the negotiations for the Cuba deal had been going on in secret, behind his back for 10 months, and said the administration had given up U.S. leverage but got nothing in return to enhance democracy or human rights.
He also delivered a veiled threat that he would use his position on Capitol Hill to thwart Obama's Cuba initiative, saying it would be "difficult" to get a U.S. ambassador to Cuba confirmed as the White House seeks to upgrade the diplomatic mission in Havana to full embassy status.
Menendez has also infuriated the White House on Iran, joining with Republican Senator Mark Kirk of Illinois in a bid to impose new sanctions on Tehran which he said would improve the administration's leverage in the talks.
The White House has fought the measure because it says new sanctions at this delicate stage of the negotiations would bolster hardline opponents of the talks in Tehran and scupper hopes for a deal.
But Menendez's influence was key this week, when he led a rearguard action to convince Senate Majority Leader Mitch McConnell not to bring up a new sanctions bill before a deadline for a framework agreement between world powers and Iran on March 24.
Still, there is no mistaking his distaste for Obama's Iran diplomacy.
In January he accused the administration of getting its talking points on the proposed deal "straight out of Tehran."