WASHINGTON >> After expressing frustration at the slow pace of approval for coronavirus treatments, President Donald Trump announced today the emergency authorization of convalescent plasma for COVID-19 patients.

The announcement came after days of White House officials suggesting there were politically motivated delays by the Food and Drug Administration in approving a vaccine and therapeutics for the disease that has upended Trump’s reelection chances.

On the eve of the Republican National Convention, Trump issued the emergency order — it would make it easier for some patients to obtain the treatment — in a news conference Sunday evening, according to White House officials.

The blood plasma, taken from patients who have recovered from the coronavirus and rich in antibodies, may provide benefits to those battling with the disease. But the evidence so far has not been conclusive about whether it works, when to administer it and what dose is needed.

In a letter describing the emergency authorization, the chief scientist for the FDA, Denise Hinton, noted: “COVID-19 convalescent plasma should not be considered a new standard of care for the treatment of patients with COVID-19. Additional data will be forthcoming from other analyses and ongoing, well-controlled clinical trials in the coming months.”

The White House had grown agitated with the pace of the plasma approval, but the accusations of a slowdown, which were presented without evidence, were just the latest assault from Trump’s team on the “deep state” bureaucracy. White House chief of staff Mark Meadows did not deal in specifics, but said that “we’ve looked at a number of people that are not being as diligent as they should be in terms of getting to the bottom of it.”

“This president is about cutting red tape,” Meadows said in an interview on “This Week” on ABC. “He had to make sure that they felt the heat. If they don’t see the light, they need to feel the heat because the American people are suffering.”

The push on Sunday came a day after Trump tweeted sharp criticism on the process to treat the virus, which has killed more than 175,000 Americans and imperiled his reelection chances. The White House has sunk vast resources into an expedited process to develop a vaccine, and Trump aides have been banking on it being an “October surprise” that could help the president make up ground in the polls.

“The deep state, or whoever, over at the FDA is making it very difficult for drug companies to get people in order to test the vaccines and therapeutics,” Trump tweeted. “Obviously, they are hoping to delay the answer until after November 3rd. Must focus on speed, and saving lives!”

Earlier this month, Mayo Clinic researchers reported a strong hint that blood plasma from COVID-19 survivors helps other infected patients recover. But it wasn’t considered proof.

More than 70,000 patients in the U.S. have been given convalescent plasma, a century-old approach to fend off flu and measles before vaccines. It’s a go-to tactic when new diseases come along, and history suggests it works against some, but not all, infections.

There’s no solid evidence yet that it fights the coronavirus and, if so, how best to use it.

The Mayo Clinic reported preliminary data from 35,000 coronavirus patients treated with plasma, and said there were fewer deaths among people given plasma within three days of diagnosis, and also among those given plasma containing the highest levels of virus-fighting antibodies.

But it wasn’t a formal study. The patients were treated in different ways in hospitals around the country as part of an FDA program designed to speed access to the experimental therapy. That so-called “expanded access” program tracks what happens to the recipients, but it cannot prove the plasma — and not other care they received — was the real reason for improvement.

Administration officials, in a call with reporters Sunday, discussed a benefit for patients who were within three days of admission to a hospital and were not on a respirator, and were given ‘high-titer’ convalescent plasma containing higher concentrations of antibodies. They were then compared to similar patients who were given lower-titer plasma. The findings suggest deaths were 35% lower in the high-titer group.

There’s been little data on how effective it is or whether it must be administered fairly early in an illness to make a significant difference, said Dr. William Schaffner, an infectious diseases expert at Vanderbilt University.

Aiming to ward off a possible a run on convalescent plasma after the announcement, government officials have been working to obtain plasma and to team with corporate partners and nonprofit organizations to generate interest among previously infected patients to donate.

The head of the FDA, Stephen Hahn, said Trump did not speak to him about the timing of the announcement, which comes just before a pivotal week for the president’s reelection chances. Hahn said “this has been in the works for several weeks” and came after a data validation for which the agency had been waiting.

Rigorous studies underway around the country are designed to get that proof, by comparing similar patients randomly assigned to get plasma or a dummy infusion in addition to regular care. But those studies have been difficult to finish as the virus waxes and wanes in different cities. Also, some patients have requested plasma rather than agreeing to a study that might give them a placebo instead.

Former FDA commissioner Dr. Scott Gottlieb dismissed the suggestion of a slowdown.

“I firmly reject the idea they would slow-walk anything or accelerate anything based on any political consideration or any consideration other than what is best for the public health and a real sense of mission to patients,” Gottlieb told CBS’s “Face the Nation.”

Hundreds of drugs are currently being developed as possible treatments against the coronavirus infection, taking a range of approaches.

Trump, in news conferences, “has made all kinds of therapeutic suggestions,” which have not proven to be supported by science — and are even dangerous, Schaffner said. That includes statements about the possible value of treating COVID-19 patients with ultraviolet light and bleach. Trump reportedly also recently became enthusiastic about oleandrin, a plant extract derived from a toxic shrub that scientists immediately warned against.

But the president is perhaps best known for his early and ardent embrace of the malaria drugs hydroxychloroquine and chloroquine.

The FDA in late March granted emergency authorization for distribution of the drugs for treating COVID. But in June, the agency revoked the authorization in light of growing evidence they don’t work and could cause serious side effects.

Not only that, the FDA warned doctors against prescribing the drugs in combination with remdesivir, a drug that was shown to help patients with COVID-19. The FDA said the anti-malaria drugs can reduce the effectiveness of remdesivir, which the FDA cleared for emergency use in May.

Earlier this month, Hahn emphasized that routine evaluation procedures will remain in place to evaluate COVID vaccine candidates.

“I think this administration has put more pressure on the Food and Drug Administration than I can remember” ever happening in the past, Schaffner said.

“Everybody is just a little bit nervous,” he said.