The Trump administration has finally picked up the pace when it comes to selecting nominees for high-level positions — but there are so many jobs that need to be filled they might "bottleneck" in the Senate, according to experts.

"What we have seen is unprecedented, with consistent vacancies across the government," said Max Stier, president and CEO of the Partnership for Public Service, a nonpartisan nonprofit that tracks presidential appointments.

There are 132 positions that have no nominee at all, including the top jobs at the Drug Enforcement Administration and the Bureau of Alcohol, Tobacco, Firearms and Explosives, the organization's data shows. There are 138 nominees awaiting confirmation by the Senate.

Trump's nominees have been proceeding at a record slow pace — averaging 105 days between nomination and confirmation. The average time for President Barack Obama's nominations to clear was 93 days — more than double that of George W. Bush's presidency.

The White House has been putting forward about 20 nominations a month since February, but has barely moved the needle in terms of filling positions. A review of the vacancies by NBC in late March showed there were then 282 openings.

In the past two weeks, President Donald Trump has announced nominations for several key posts, most notably acting Defense Secretary Patrick Shanahan and Mark Morgan as Immigration and Customs Enforcement director. The White House on Monday also officially nominated Jeffrey Byard to head the Federal Emergency Management Agency, almost three months after Trump first named him as his pick.

Despite the forward motion, the Trump administration still has vacancies in 277 top positions out of just over 700 appointments that require Senate confirmation, according to an online tracker by the Partnership and The Washington Post.

One reason the improvement is so incremental is because of the continued turnover in the administration, Stier said. Last month, the president pushed out Homeland Security Secretary Kirstjen Nielsen, and named Customs and Border Protection head Kevin McAleenan acting head of the agency — creating another opening in Customs.

"There's still an element of musical chairs — filling one job and creating a vacancy somewhere else," Steir said. That causes "cascading effects. Somebody leaves, others follow. You're creating disruptions throughout the whole organization."

While Trump has blamed the pace of confirmations on the Democrats, Chris Lu, a senior fellow at the University of Virginia Miller Center and former White House Cabinet secretary in the Obama administration, said each nomination eats up a large amount of manpower.

"It's chewing up a huge amount of time in these agencies and in the U.S. Senate," said Lu, who's gone through the nomination and confirmation process. "Federal agencies are like big ocean liners — you need time to move them."

And the waters they've been sailing in have been choppy, thanks to the high amount of turnover at the top.

Fifteen members of Trump's Cabinet who were confirmed by the Senate have resigned, been pushed out or fired, according to an analysis by the Brookings Institution — meaning all those positions have to be filled and confirmed again.

The process is a "churn that takes up energy in the Senate, in the personnel office and the agencies themselves," Lu said, recalling that he had "a whole team come together" to help get him prepared for hearings to be deputy secretary of Labor, even though unlike many of Trump's picks, his nomination wasn't controversial.

In addition, 61 of Trump's nominations have been withdrawn, the Partnership found, more than double the amount of nominations pulled back in the same time span in the Obama administration.

And that figure does not include those like Stephen Moore or Herman Cain, both of whom Trump said he wanted for the Federal Reserve board but were never formally nominated before backing out after it became clear they wouldn't be confirmed by the Republican-controlled Senate.

Lu predicted the administration would have a hard time filling positions in some agencies, like the Department of Homeland Security, which oversees FEMA, ICE and CBP and where nine out of 17 Senate-confirmable posts are either lacking a nominee or waiting for a nominee to be confirmed.

All the nominees will have be confirmed through the same Senate committee.

"That's a pretty big bottleneck right there," Lu said. "It's not going to get any easier. It's not like the Senate is going to be in session a lot, especially in an election year."

Stier added: "The system is on overload. You have too many people trying to get jammed through the Senate."