WASHINGTON — Facing a potentially devastating Democratic defection in the Senate, the White House is ramping up its fight to confirm an embattled judicial nominee who would be the first Muslim American to serve as a U.S. federal appeals court judge.

The White House is touting a wave of new law enforcement endorsements for Adeel Mangi to the 3rd U.S. Circuit Court of Appeals, building on seven similar organizations that have already backed Mangi, in an attempt to counter what it describes as a Republican-led smear campaign predicated on his religion.

“Some Senate Republicans and their extreme allies are relentlessly smearing Adeel Mangi with baseless accusations that he is anti-police,” White House chief of staff Jeff Zients said in a statement to NBC News. “That could not be further from the truth, and the close-to-a-dozen law enforcement organizations that have endorsed him agree.”

On Wednesday, a third Democratic senator came out against Mangi’s nomination: Jacky Rosen of Nevada, who joined her home state colleague, Sen. Catherine Cortez Masto, D-Nev., and centrist Sen. Joe Manchin, D-W.Va., in opposing him. The move puts Mangi’s nomination in greater peril in the Senate, where Democrats hold a 51-to-49 majority.

Behind the scenes, Zients and other top White House officials have been pushing lawmakers to confirm Mangi “without further delay,” a White House official said. In addition to Zients, White House Legislative Affairs Director Shuwanza Goff, Deputy Legislative Affairs Director Ali Nouri, White House counsel Ed Siskel and Phil Brest, the White House senior counsel in charge of nominations, have all been in regular touch with senators, the official added.

Mangi’s embattled nomination presents a political conundrum for President Joe Biden as he dials up his re-election campaign. The White House’s relationship with Muslim Americans has grown sour amid the community’s strong disapproval of U.S. support for Israel as it bombards Gaza. Biden is counting on strong support this fall from the Democratic-leaning cohort, which represents a sliver of the U.S. electorate but has a significant presence in some states, most notably battleground Michigan.

In new statements shared by the White House, three former New Jersey attorneys general and two former U.S. attorneys who served in the state expressed their support for Mangi, in addition to the International Law Enforcement Officers Association and the Italian American Police Society of New Jersey. The National Organization of Black Law Enforcement Executives has also come out in support of Mangi. 

“Mr. Mangi has displayed the qualities of leadership, empathy, excellence, and persistence in supporting and defending the U.S. Constitution while ensuring equal protection and justice for all Americans,” the group wrote in a letter to congressional leaders last week.

Rosen, who faces re-election in the competitive state of Nevada, announced her opposition to Mangi on Wednesday evening. “Given the concerns I’ve heard from law enforcement in Nevada, I am not planning to vote to confirm this nominee,” she said in a statement provided by her office.

The Judiciary Committee approved Mangi on a party-line vote in January. He needs the support of 50 senators to be confirmed. No Republicans have said they’ll support him, although some haven’t said how they’d vote if he comes up on the Senate floor.

Republicans have attacked Mangi for his affiliation with the Rutgers Law School Center for Security, Race and Rights, chastising its decision to host an event featuring a speaker named Sami Al-Arian, who in 2006 pleaded guilty to conspiracy to assist the designated terrorist group Palestinian Islamic Jihad, according to the Justice Department. Mangi told the Senate in written testimony he had “no involvement” in the Rutgers Center speaker events.

The 3rd Circuit vacancy creates another dilemma for Biden: Democrats have only nine more months of guaranteed control of the White House and the Senate to fill the powerful seat without requiring any Republican help. If Mangi can’ be confirmed, withdrawing his nomination sooner rather than later would make it easier for Biden to find and steer another nominee through the Senate. But if he’s perceived as abandoning Mangi without a fight, it could backfire with some voters.

In recent weeks, senior White House officials have slammed Republicans for “cruel and Islamophobic attacks’’ as part of a larger “smear effort” to discredit Mangi.

Manchin said Friday he’s “not voting” for Mangi because he’s not a “reasonable” nominee to be a life-tenured judge. He called him “out of my wheelhouse.” The same day, Cortez Masto said in an interview that she hasn’t heard from Democratic leadership about Mangi since she came out against him and that she remains committed to opposing him.

That means he’ll need Republicans to rescue his nomination unless at least one of his Democratic opponents reverses course.

Centrist Sen. Lisa Murkowski, R-Alaska, who sometimes breaks with her party on judges, said she hasn’t evaluated Mangi’s nomination.

“I still have not looked at it, because he’s not been brought up,” she said, adding that she would evaluate Mangi “the same way that I have looked at every single judicial nominee that’s come in front of me since 2010, which is: Are they qualified?”