Medical manufacturers large and small have spent weeks ramping up production of the expensive, lifesaving machines that can breathe for critically ill patients. Last week, President Trump vaguely invoked the Cold War–era Defense Production Act, asking automakers and other companies to help make ventilators and other medical supplies—though he has so far stopped short of wielding the law’s full powers to order more ventilator production. General Motors, Ford Motor, and Tesla have all said that they are trying to chip in by partnering with medical-device manufacturers, while the U.S. Food and Drug Administration over the weekend relaxed some guidelines to ease their way.

But ventilator industry executives and experts warn there is a limit to how much these emergency measures—or even greater federal assistance—could speed up production, especially in time for the rapidly growing hospitalizations of U.S. coronavirus victims. The grim reasons come down to the necessary regulations involved in medical manufacturing, ongoing supply-chain problems, and a shortage of trained personnel who know how to use the complex, life-or-death machines.

“It is not a question of throwing enough money and people at the issue,” says Bob Hamilton, the CEO of Hamilton Medical Inc., the U.S. subsidiary of Swiss-based Hamilton Medical AG.

“Ventilators are highly specialized lifesaving machines that need to be built with the utmost care and precision,” he adds, in an emailed response to questions from Fortune. “So it needs trained people to do it, and it needs time.”

Hamilton Medical makes 15,000 ventilators annually, and has already said it’s ramping up overall production by up to 40%. Hamilton adds that he plans to at least double the production of the company’s “most needed” transportable ventilators, which can be used in intensive care units and elsewhere. Those two models, the Hamilton-T1 and the Hamilton-C1, together accounted for more than half of the ventilators it made last year, the company said.

Competitors including Medtronic, General Electric, Getinge, Philips, and Dräger also make hospital-grade ventilators, which can cost between $25,000 and $50,000 each. But the U.S. has fewer than 175,000 of them, including about 12,700 in the government’s National Strategic Stockpile. That’s far short of the estimated 1 million ventilators the country’s hospitals may need for coronavirus cases alone, according to some calculations.

Now politicians, health care officials, and executives across several industries are working to supply more breathing machines to already stretched hospitals—and to avoid the tragic shortages seen in Italy. But even under the best possible circumstances, manufacturing enough of the lifesaving machines for American needs will be a matter of months, not weeks, experts warn.

If President Trump invokes the Defense Production Act to specifically order more ventilators and open new lines, “a production increase would take at a minimum 90 days, even if you have every part and everything you need,” says Julie Letwat, a health care lawyer with McGuireWoods in Chicago.

“But anything you say is a moving target,” she adds. “It also depends on employees coming in and not getting sick,” when “one COVID-positive test could clear a manufacturing floor.”

Procurement problems

For ventilator manufacturers, obtaining enough necessary parts and materials is a widespread industry challenge, made even more acute as the global nature of the supply chain is colliding with the global nature of the coronavirus pandemic.

“The biggest threat is that our suppliers cannot ramp up their production accordingly, because their supply chains are interrupted or are hindered by export restrictions,” says Hamilton.

His company has already faced one such minor incident: Romania restricted exports of medical products, meaning that Hamilton Medical couldn’t receive some expected humidifier supplies. Hamilton says the problem was resolved “quickly,” but he’s now worried that other countries could “do the same, and that might interrupt our supply chain.”

His company, founded in 1983, is one of several established ventilator manufacturers that have been working overtime since the emergence of COVID-19 in China late last year. Hamilton says he has hired additional employees, retrained existing staff, and kept production going through the weekends.

But he is not yet working with a car manufacturer—and sounds skeptical about the efficacy of doing so, even as some of his competitors team up with the likes of GM and Ford.

“It is not enough just to screw the devices together. They must also be tested accordingly. And every medical manufacturer in the U.S. needs approvals by the FDA, which are not easy to obtain,” Hamilton says. “In our opinion, it is far more efficient to expand production where the know-how and approvals are already available.”

In the past few days, General Motors has said it is partnering with Ventec Life Systems to help the small ventilator company increase production and to “leverage GM’s logistics, purchasing, and manufacturing expertise.” Ford announced it is working with GE Healthcare “to expand production of a simplified version” of the latter company’s ventilators, and Elon Musk has, of course, tweeted about having “engineering discussions” with Medtronic. (The Tesla CEO also helped buy more than 1,200 ventilators from China and donated them to officials in Los Angeles.)

But it’s unclear how quickly most of these discussions or partnerships can yield physical results. “We’re talking about early June,” Ford CEO Jim Hackett said on Tuesday.

And many industry experts warn that it’s optimistic—and potentially dangerous—to expect car manufacturers to switch their production lines over to medical devices swiftly or easily.

“It doesn’t really matter if your phone doesn’t work, because it wasn’t put together right,” says Marcus Schabacker, a physician and the CEO of ECRI, a nonprofit patient-safety organization that tracks medical devices. “If your ventilator doesn’t work because it wasn’t put together right, that’s a problem.”

Relaxed regulations

The Food and Drug Administration on Sunday temporarily loosened some guidelines for ventilator manufacturers, granting manufacturers more flexibility to make changes to suppliers or materials, and making it easier for automakers to repurpose their production lines.

“They have the people, and they have the factories,” says Madris Tomes, a former FDA employee who now tracks medical-device industry data at her Device Events firm. “There are certain parts of making ventilators where they can definitely” step in.

Still, Tomes and other experts warn that the FDA’s restrictions on medical-grade materials, devices, and processes exist for good reason: Like a rushed and potentially lethal vaccine, a rushed and potentially dysfunctional breathing machine can be worse than useless.

“If [ventilators] are not properly developed, designed, manufactured, and operated by skilled clinicians, you can kill a patient,” says Patrick Keane, an intellectual property lawyer at Buchanan Ingersoll & Rooney who works with Hamilton Medical. “You have to be really careful about how they’re manufactured, how they’re put into practice, and then how they’re actually used.”

Xu Gang, managing director and partner at the Boston Consulting Group who leads BCG’s automotive sector in Greater China, is more optimistic. Big automakers are “quite a good fit” for ventilator production, Xu says, because of their experience in large-scale manufacturing, established quality control mechanisms, and a skilled labor force.

“I think fundamentally they will be able to do it,” Xu says. Still, he adds, workers will need retraining, and factory plants will likely need to be retrofitted before they can start making ventilators or ventilator parts.

Schabacker adds that he expects the loosened FDA guidance will help—eventually. “It will be easier to make parts and components,” he says. “But it will still not be a quick fix.”