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When the federal mandate requiring masks to be worn on planes and other public transportation crumbled last week, it was not because of lobbying by established trade organizations, or even a determination by the Centers for Disease Control and Prevention that masks were no longer necessary.

The demise of the mask mandate was brought about by an unlikely confluence of individuals: a former Wall Street analyst living in Idaho who founded an anti-covid-regulation nonprofit, and two Florida women who said their anxiety prevented them from wearing masks.

Flight attendants, pilots and passengers were free to fly without masks, and public transit systems across the country were free of masks, after a judge ruled that the federal government had overstepped its authority by requiring masks. The people who had been watching the effort to overturn the rule were surprised.

The president of the American Society of Travel Advisors said it was a shocking event.

The American Public Health Association's executive director, Dr. Georges C. Benjamin, called the ruling "unmaginable" and "causing announcements mid-flight"

The back story of the judge's decision offers a glimpse into the way public health policy in the United States is made, in which a lawsuit filed by a little-known organization that opposed masks and vaccine mandates can upend a rule crafted by doctors and scientists.

Anne Sosin is a public health policy fellow at the college.

The other women in the case are in Florida. The ties that bind them seem to be the anxiety and distrust caused by wearing a mask.

According to the complaint, Ana Carolina Daza, who lives in the Tampa Bay area, was hoping to visit her family in Colombia last August, but could not imagine doing so if she had to wear a mask.

According to the complaint, Ms. Daza feels like she can't breathe when she wears a mask.

Sarah Pope lives in the Tampa Bay area. She decided not to join her family on a trip to Hawaii because of the thought of wearing a mask for a long flight.

According to an interview with Ms. Manookian, Ms. Daza and Ms. Pope paid $10 to join her organization over the past two years.

The Health Freedom Defense Fund says on its website that it stands for choice and bodily autonomy.

Ms. Manookian said that she was concerned about the vaccine rules and began to feel angry.

She said that she saw "very strident measures being taken, which violated, I think, basic American liberties." She founded her organization to educate the populace about their rights and to help them file lawsuits whenever their rights were violated.

The transportation mask mandate was one of the first things Ms. Manookian decided to do. More than a dozen lawsuits against vaccine mandates have been filed by the group.

Ms. Manookian said that her legal team advised her to file in the conservative division of the Federal District Court for the Middle District of Florida. Legal experts say that this was a good choice because five of the six active district court judges in that division were appointed by Republican presidents.

According to court documents, the team was led by a Miami attorney who is also a specialist in drone law. He was joined by a lawyer from New Orleans who worked for the Federal Trade Commission in the Reagan era and who sometimes represents America's Frontline Doctors, an activist group that spreads misinformation about Covid vaccines. Both didn't want to comment.

The team needed at least one person who lived in the district to file.

Ms. Manookian hung up when she was asked about how she learned about Ms. Daza and Ms. Pope. She said that they were members of her organization.

She said that she was able to expand her membership because of the community she built around her documentary film.

The film intersperses stories of lives destroyed by vaccines with interviews from scientists in agencies, including the C.D.C., and more questionable experts. Science-Based Medicine is a website that reports on pseudoscience and other health frauds.

Ms. Pope has a self-published book, has a YouTube channel, and writes about home remedies and healthy eating.

She gave an interview to The Daily Show in which she claimed that vaccines are full of toxins.

Ms. Pope said that she was not going to change her mind.

She worked on Wall Street in the 1990s and early 2000s. She got a ton of travel vaccines when she was 28, which led to a ton of health problems.

When Ms. Pope and Ms. Daza filed their lawsuit, they were assigned to the newest judge in the division. It was a good thing.

Lawrence O. Gostin is a professor of global health law at Georgetown University.

They fought to keep the winning ticket. The lawyers representing the C.D.C. and the White House wanted the case to be heard by a different judge in the same district. The cases were different and the judge denied the motion to transfer.

The C.D.C. extended the mask mandate by two weeks on the day it was scheduled to expire. The Public Health Service Act of 1944 gives federal officials the authority to make and enforce regulations to prevent the introduction of a communicable disease from foreign countries and its spread between states. The law states that the authorities may impose regulations that include inspection, fumigation, and other measures.

In deciding whether or not the C.D.C. had overstepped, Judge Mizelle focused on the word "sanitation" and ruled that mask-wearing didn't meet a definition she found in several dictionaries. She wrote that Sanitation refers to measures that clean something.

Mr. Gostin said that a judge might have skipped the focus on Sanitation altogether because the law also allows for other measures. The judge might have taken a different view of the word.

Even though it is not consistent with the way that it has been used in public health law for centuries, she interprets it in a narrowest way.

Critics have focused on the fact that the American Bar Association deemed Judge Mizelle not qualified for a life-tenured judicial seat because she was just 33 when Mr. Trump appointed her.

Judge Mizelle was a member of the conservative legal movement. She clerked for Supreme Court Justice Clarence Thomas after graduating from law school.

She said he was the greatest living American because he had taken a commitment to originalism.

In May 2020 she helped business interests argue against a proposal for mandatory federal workplace safety standards to protect workers against Covid-19 infections.

The C.D.C.'s powers to take necessary actions in a public-health crisis were the subject of an appeal by the Biden Administration. A majority of the judges on the 11th Circuit are also appointees of the president.

A ruling by the appeals court backing Judge Mizelle's interpretation of the Public Health Service Act of 1944 would be a binding precedent. The Justice Department could ask the appeals court to dismiss the case, and even erase the judge's ruling, if it wanted to, because the mandate was set to expire on May 3.

There would be no ability for federal administrative agencies to regulate interstate transit in other ways in a public health emergency if it stands. She said that the ability to issue rules was what the Trump administration was hoping to lock into place.