President Donald Trump is struggling to fill out hundreds of government jobs, and the task isn’t getting any easier in a hectic White House.

Just over four months into his administration, Trump has lagged far behind recent administrations in getting executive branch officials confirmed by the Senate — or even nominating anyone for the jobs. Those include critical positions, such as deputy and assistant Cabinet secretaries, some of whom would presumably help craft the president’s ambitious policy agenda.

Trump is early in his first term and has time to fill out the government. But in a lean White House pushing for a flurry of legislative activity and shadowed by an FBI probe, getting skilled individuals nominated and confirmed could prove difficult, according to people who follow the presidential appointment process.

“Once you fall behind, it’s very hard to catch up … there are a lot of competing priorities. The urgent can crowd out the important. There are things to deal with like the Russia investigation and health care reform,” said Max Stier, president and CEO of the Partnership for Public Service, a nonprofit that tracks the pace of presidential nominations.

The White House did not immediately respond to a request to comment on this story.

As of Wednesday morning, the president had formally nominated only 110 people to roughly 1,200 positions that require Senate confirmation, with 40 appointees confirmed, according to the Partnership for Public Service. He lags far behind the pace set by Barack Obama, George W. Bush, Bill Clinton and George H.W. Bush, who had all seen at least twice as many appointees confirmed by May 31 of their first terms.

In the group of 559 jobs the Partnership for Public Service classifies as higher priority Trump has nominated 63 people and seen 39 of those confirmed. Other presidents have taken time to fill out their administrations, but Trump is going even more slowly.

“Prior presidents haven’t done this well, and Trump is doing worse than they did,” Stier said.

Those figures do not include the more than 100 federal court vacancies that Trump is supposed to fill. Trump announced a group of 10 nominees to those seats early this month and is expected to choose more judges in the coming months.

Several factors have contributed to Trump’s slower pace filling out positions, according to Anne O’Connell, a law professor at the University of California, Berkeley, who has studied the presidential appointment process. Some of the struggles relate to “self-harm,” such as not taking enough time to vet nominees who later withdrew, or ruling out candidates who made critical statements about Trump statements in the election, she said.

Government hiring has also put constraints on Trump that the private sector did not when he worked as a businessman, O’Connell said.

Trump also never held elected office. A lack of executive branch experience, in particular, has slowed presidents who did not previously serve there, she said.

O’Connell noted, however, that Trump has picked up his pace of appointments since his 100th day in office in April.

Trump faces another major problem in finding appointees: Candidates are reluctant to take the jobs.

The White House is trying to distance itself from the FBI’s investigation into Russian interference with the U.S. 2016 election and possible ties between the Trump campaign and Moscow. Trump’s firing of FBI Director James Comey and questions about his motives have only complicated matters for his top advisors, many of whom are balancing a slew of responsibilities.

That’s an environment many top candidates hesitate to enter, experts said. Some candidates who would normally see White House jobs as a gem on their resumes no longer do.

“They won’t be able to attract the most talented people in Washington D.C. Nobody in the right mind would jump into this White House at this point. I don’t think it’s a very positive work environment right now for anybody to take the leap here,” said Steven Billet, director of the masters program in legislative affairs at George Washington University’s Graduate School of Political Management.

A New York Times report Tuesday said the White House has had difficulty finding a replacement for recently departed communications director Michael Dubke. The FBI probe “coupled with the president’s habit of undercutting his staff” have “driven away candidates for West Wing jobs that normally would be among the most coveted in American politics,” the newspaper reported.

The White House’s troubles make “what was already really hard even harder,” said Stier from the Partnership for Public Service.

In another recent example, Goldman Sachs executive Jim Donovan, the nominee for the No. 2 spot at the Treasury Department, dropped out of contention this month. Donovan cited a desire to focus on his family. Trump has not announced a new nominee.

The Republican-controlled Senate, which confirms Trump’s appointments, also faces a packed legislative schedule, leaving it less time to take up nominations. This year, the chamber will aim to craft plans to overhaul the American health care and tax systems, pass an appropriations bill and raise the federal debt limit.

On top of that, Democrats emboldened by resistance to Trump have worked to delay many of his nominees, though their ability to do so is limited.

Stier and Billet note that a lack of appointments could affect a range of policy decisions. That includes Trump’s big-ticket goals like overhauls of the American health-care and tax systems.

For example, career officials at the Treasury Department are working on tax policy. But having another high-level official working with Treasury Secretary Steven Mnuchin on tax reform could bring new insight or policy ideas that the administration currently lacks.

“Decisions don’t get made as well, as quickly or as effectively without a presidentially-appointed, Senate-confirmed, person in place,” Stier said.

Billet noted that the debut of Trump’s tax plan in April came in the form of a one-page summary. Congress “needs something more than that” if the White House “wants to play a leading role” in the tax legislation that lawmakers eventually take up, Billet said.

Berkeley’s O’Connell notes that institutions like the Federal Energy Regulatory Commission and Nuclear Regulatory Commission also suffer without appointees.