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WASHINGTON — President Donald Trump's decision to downsize the White House national security staff — and eliminate jobs addressing global pandemics — is likely to hamper the U.S. government's response to the coronavirus, according to veterans of past disease outbreaks and experts who have studied them.

"This is why you have a National Security Council," said John Gans, a former Pentagon speechwriter who wrote a book about the NSC, which has long been the principal advisory body inside the White House for national security affairs. "The changes have made it much harder for the NSC to do this."

Health and Human Services Secretary Alex Azar is leading the Trump administration's coronavirus response efforts. On Wednesday, Azar disputed reports that Trump would soon be appointing a coronavirus "czar," or response coordinator.

"I don't anticipate one," Azar said at a House Appropriations Committee hearing. "This [strategy] is working extremely well."

However, one former Trump senior official said a czar — and not a Cabinet secretary — was needed to run the administration's response. "It's better to have one person who has the backing of the White House to coordinate," the official said.

Veterans of the Ebola virus outbreak of six years ago also fear Azar is speaking too soon.

In 2014, as the U.S. government scrambled to respond to the Ebola outbreak, President Barack Obama appointed lawyer Ron Klain to lead the effort from the White House, supported by staff from the National Security Council.

Participants recall it as the most intense, most difficult thing the Obama White House ever took on. They said the NSC was the only power center that could harness and coordinate the many federal government agencies implicated, foreign and domestic.

"The Ebola response in the Obama National Security Council was the most frenetic, the most tireless operation that I was a part of, and I was there for the counter-ISIS campaign and the Iran nuclear deal," Ned Price, a former CIA officer and an Obama White House staffer, said.

"A pandemic is inevitable; the remaining question is how severe will it be."

"The NSC is the only place at the fulcrum of foreign policy where you can also pull the levers of domestic policy. ... What we found was that there was a degree of running in circles until the White House National Security Council staff began directing the effort."

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In 2018, Trump fired Tom Bossert, whose job as homeland security adviser on the NSC included coordinating the response to global pandemics. Bossert was not replaced. Last year, Rear Adm. Tim Ziemer, the NSC's senior director for global health security and biodefense, left the council and was not replaced. Dr. Luciana Borio, the NSC's director for medical and biodefense preparedness, left in May 2018 and was also not replaced.

In an October op-ed in The Washington Post, national security adviser Robert O'Brien described the Obama National Security Council as having "ballooned to well over 200 staffers," and he said he intended "to reduce the NSC staff."

Said a former senior U.S. official, "For the first time since 9/11, you don't have someone directly and immediately reporting to the president responsible 24/7 for the major transnational threats we face — terror, cyber, pandemics."

Major challenges loom, public health experts say.

One immediate problem, Dr. Borio told NBC News, is that there is not yet a foolproof test to determine who has the virus.

"Having a good diagnostic test is necessary to protect health care workers so they can perform their work and it is also essential to understand the epidemic trajectory," she said. "A good diagnostic test is important so you can conduct good tests for therapeutics and a vaccine, it underpins a lot of the other components."

"I'm concerned with the fact that we are not yet doing testing on individuals with unexplained respiratory illness, to detect whether the virus is already circulating in the community."

"As the disease spreads geographically, the travel measures become less effective and more disruptive," Borio said. "A pandemic is inevitable; the remaining question is how severe will it be."

Jeremy Konyndyk, who led foreign disaster assistance at the U.S. Agency for International Development during the Obama administration, said the administration should have acted earlier in coordinating with hospital systems and local health departments.

"That has not happened until the last few days, we have lost a lot of time," he told NBC News. "Putting some passive guidance on the [Centers for Disease Control and Prevention] website is very different from saying you need to begin conserving and rationing personal protective equipment or you need to triage health care."

After being briefed on Capitol Hill, some lawmakers have expressed concern.

Sen. Mitt Romney, a Utah Republican, questioned why there were eight officials in the briefing he received.

"And I'd note that this is probably something that justifies having one person in government who can work across the various departments and agencies to make sure we have a unified response to protect our citizens," he told reporters.

In response to a Trump administration request this week for $2.5 billion in emergency funding, House Speaker Nancy Pelosi tweeted, "Americans need a coordinated, fully funded, whole-of-government response to keep them and their loved ones safe. The President's request for coronavirus response funding is long overdue and completely inadequate to the scale of this emergency."

Last week, according to a notice in the federal register, the Centers for Disease Control and Prevention (CDC), a component of the Department of Health and Human Services (HHS), ordered airlines to collect and provide information about any passenger who has departed from, or was present in China, within 14 days of the person's entry into the U.S. No further notices have been posted on data collection for flights from Iran or Italy, however.

The U.S. must immediately stop all flights from EBOLA infected countries or the plague will start and spread inside our "borders." Act fast! — Donald J. Trump (@realDonaldTrump) August 2, 2014

Trump has said the media is hyping the severity of the coronavirus. In 2014, during the Ebola outbreak, he took a much different view, criticizing Obama.

"The U.S. must immediately stop all flights from EBOLA infected countries or the plague will start and spread inside our 'borders,'" he tweeted in August 2014. "Act fast!"

In November of that year, he called Obama "psycho" for not immediately closing the U.S. to flights from abroad.

I am starting to think that there is something seriously wrong with President Obama's mental health. Why won't he stop the flights. Psycho! — Donald J. Trump (@realDonaldTrump) October 16, 2014

While much more lethal than coronavirus, Ebola does not spread nearly as fast or easily.

Federal public health officials warned Tuesday that the spread of coronavirus in the U.S. is "inevitable."