The U.S. Occupational Safety and Health Administration will likely have to move forward without a new leader until after the 2020 presidential election after President Donald Trump’s nominee withdrew his candidacy — disappointing employer representatives who had hoped for a less combative relationship with the agency.

The president nominated Scott Mugno, then-vice president for safety, sustainability and vehicle maintenance at FedEx Ground, a unit of FedEx Corp., as assistant secretary of OSHA in October 2017, but his nomination stalled for 19 months amid partisan disagreements. The withdrawal, reported by Bloomberg Law, has not been officially confirmed by the White House, but Mr. Mugno has updated his LinkedIn page to remove a reference to his awaiting Senate confirmation and replacing it with a reference to his nomination with a May 2019 end date and updating his current status to board member at Franklin County Water Service Authority in Russellville, Alabama.

Employers had been hoping for a more collaborative relationship with the agency under Mr. Mugno’s leadership.

“I’m disappointed because I thought he had the ability, or at least the potential, to bring the agency back to where it belonged,” said James Curtis, a Chicago-based partner in law firm Seyfarth Shaw LLP’s environmental safety and toxic torts practice group. “We had seen a lot of damage under the prior administration from an employer’s perspective, and there was a lot of hostility within the agency from the prior administration towards employers.”

Loren Sweatt, deputy assistant secretary of labor for OSHA, has been running the agency on an acting basis, and she will have to continue to head OSHA for the foreseeable future, experts say.

“I don’t think there will be a head of OSHA under the Trump administration unless he wins reelection and he gets another four-year term,” Mr. Curtis said.

“I wish the administration the best of luck in finding a nominee,” said John Martin, a Washington-based shareholder and national OSHA counsel with Ogletree, Deakins, Nash, Smoak & Stewart P.C. “I’m not sure who would be willing to do it at this point, considering you’ve got 18 months from now until the 2020 presidential election. Even if all the planets aligned and you were able to push through to confirmation, even in the best of circumstances that would probably happen six months from now. That gives you basically a year in office to do something, and that’s not much time to leave a legacy or do much of anything within a federal agency.”

The slowness in confirming presidential employees to federal agencies was not limited to OSHA, experts noted. For example, President Trump had nominated Daniel Gade to a vacant spot on the U.S. Equal Employment Opportunity Commission, but he withdrew his nomination in December 2018 after the Senate failed to vote on it for more than a year.

“This is not an issue that only OSHA is dealing with,” said Raymond Perez, of counsel and a labor and employment attorney in the Atlanta office of Jackson Lewis P.C. “This is a common thing that’s going on throughout a lot of the different agencies, whether there are all these vacancies or people in acting or temporary roles. It leaves the agency without any real direct leadership to focus on the priorities of the administration.”

A procedural change in April that limits hours of Senate debate to two hours instead of 30 hours was expected to speed up confirmation of some agency nominees, including Mr. Mugno, experts say.

“I don’t think there was any specific objection to him,” Mr. Curtis said. “In fact, I think it was widely believed that he was one of the better nominations coming out of the Trump administration. But the Congress has become so partisan and so dysfunctional that the way they are proceeding with bringing nominations to vote is just not working any longer.”

Not having a confirmed political leader has meant the agency has largely kept pace with the enforcement activity seen during the Obama administration despite a decline in the number of inspectors, experts say.

“Certainly, in my practice, I haven’t noticed any big changes in what we’re seeing out of the area offices in terms of citations and other enforcement activities,” said Taylor White, Dallas-based senior counsel for Foley & Lardner LLP who advises employers on workplace safety and other issues. “In a couple of instances, they’ve been even more aggressive than I’ve seen them in the past.”

For example, OSHA received 9,135 of hospitalizations of injured employees in 2018, 27% of which resulted in an inspection of the workplace, under its severe injury reporting rule. By comparison, the agency received 8,063 such reports in 2017, 25% of which resulted in inspections.

“From our experience within the past two years, we’ve seen enforcement continue at a steady pace,” Mr. Perez said. Not having a confirmed leader “hasn’t had any impact on the frequency of inspections or follow-ups, especially in cases of fatalities or amputations or other serious injuries. We haven’t seen a decline in enforcement actions or citations or in litigating cases.”

“There’s a general thought in the employer community — is this hamstringing the onset of a little bit more lenient enforcement of safety standards, of what we would think the Trump administration would otherwise want to do,” Mr. White said. “Companies are obviously concerned about whether we’re still seeing and operating under the stricter enforcement standards of the Obama era.”

Employers had hoped the agency would pull back on some of the more controversial regulatory efforts under the Obama administration, including the agency’s electronic record-keeping rule. For example, OSHA amended the 2017 regulation by rescinding the requirement for establishments with 250 or more employees to electronically submit information from OSHA forms 300 and 301, but these establishments are still required to submit information from their Form 300A summaries, including confidential business information.

“It continues to put the agency on not very stable ground in terms of moving forward with the new administration’s efforts to try to have deregulation and less enforcement action and working more on compliance issues with employers,” Mr. Perez said. “It seems like the current status quo will continue without any further guidance or any real change in the directives or policies. The agency is not going to be able to move forward with any substantive rule changes or enacting new policies for heat stress or workplace violence.”