New Jersey Gov. Chris Christie walks to his vehicle after being sworn in for his second term as governor in  Trenton, N.J., on Jan. 21. (Lucas Jackson/Reuters)

New Jersey Gov. Chris Christie faces an immediate and ongoing threat to his career as federal investigators ramp up inquiries into political retribution that happened under his watch and legislative Democrats issue subpoenas. But the prospective presidential candidate will soon have to confront a longer-term challenge to his political future: He just lost the adviser who was supposed to manage his campaign.

Bill Stepien, the former top Christie aide who piloted the governor’s 2013 reelection campaign, is one of 17 individuals who received a subpoena demanding documents and testimony in connection with a bogus traffic jam on the George Washington Bridge last month. E-mails obtained by The Washington Post showed Stepien corresponding with David Wildstein, a top appointee to the Port Authority of New York and New Jersey who resigned amid growing fury over the lane closures.

Stepien, a former top official at the Republican National Committee with experience on two presidential campaigns, had been expected to manage Christie’s bid in 2016. But in the wake of the scandal, Christie told Stepien not to apply for a position atop the New Jersey Republican Party or at the Republican Governors Association, which Christie chairs this year.

That decision shocked New Jersey political insiders, given how integral Stepien had been to Christie’s rise. Now, it leaves Christie’s team searching for a new presidential campaign manager — a position almost uniquely difficult to fill.

That’s because, simply put, there aren’t that many people qualified to take on a national campaign.

“Being a campaign manager is like getting a masters in politics. Until you’ve actually done it and worked intimately close to it, [and] there’s only a handful of those people … you don’t know what you don’t know,” said Michael Biundo, a Republican operative who managed former Sen. Rick Santorum’s 2012 campaign. “I learned more during that process than I ever would have expected to. It’s nothing like running a statewide campaign.”

Making matters more difficult for Christie, most of his would-be rivals have already settled on campaign managers, further depleting the talent pool.

“It’s one of the structural challenges that we face in our party. There’s just a paucity of talent up and down the board,” said one top Republican operative who admires Christie. “Finding good campaign managers at the statewide level, and a lot of cases at the congressional level, is really hard. There’s been a bit of a strategic talent shortage in the GOP.”

Sen. Marco Rubio (R-Fla.) is likely to turn to Terry Sullivan, a longtime South Carolina operative. Louisiana Gov. Bobby Jindal is likely to ask Timmy Teepell, who managed his gubernatorial campaigns and who is a partner at OnMessage Inc., the prominent Virginia-based Republican consulting firm. Wisconsin Gov. Scott Walker has Keith Gilkes, his longtime political hand. Both Sens. Ted Cruz (R-Tex.) and Rand Paul (R-Ky.) are likely to choose longtime advisers. And Santorum, should he run again, will lean on a team led by John Brabender in a strategic consulting role.

Christie’s top political adviser, Mike DuHaime, is likely to serve in a senior strategist role in an eventual presidential campaign. But the new manager’s identity is less clear. Several operatives who have worked with Christie’s team pointed to two possible replacements: Rick Wiley, a former political director at the Republican National Committee who now works at DuHaime’s firm, and Jason Miller, a consultant who works for the firm that created Christie’s ads during the 2013 campaign.

Others who might get a phone call from Trenton include several operatives with experience running national party committees. Those interviewed for this story, most of whom spoke on the condition of anonymity, named Phil Cox, the current executive director of the RGA; Phil Musser, a former RGA director; and Rob Jesmer, who headed the National Republican Senatorial Committee for two cycles.

Republican operatives highlighted other names as well, including Gentry Collins, a former RNC political director; Carl Forti, a top official at American Crossroads; Sara Fagen, who served as political director under President George W. Bush; and Terry Nelson, who briefly managed John McCain’s 2008 campaign.

Several of those on the top rungs of the management ladder either have ties to other candidates or are involved in lucrative consulting businesses. Potential managers who have not spent years getting to know Christie, and earning his trust, would have to be presented with a hefty contract to take so much time away from their businesses.

“It would take a heck of an opportunity for me to quit my day job and go work on a two-year presidential campaign,” said the top operative, whose name has been floated as a possible manager.

Whoever joins Christie’s team will have to spend time earning the candidate’s trust. Some candidates gel quickly with their managers; campaigns in which the relationships aren’t as close can devolve into infighting and name-calling, unnecessary distractions that can hurt the cause.

Christie, whose political team is said to be cohesive almost to a fault, has been urged by fellow Republicans to expand his circle of advisers.

“Sometimes, if you’ve had a team around you your whole career and you have to look for a new team, or you’re switching horses in the middle of a race, from a chemistry standpoint that’s difficult,” Biundo said. “Finding [the right] person will take some time and effort.”