DFW customs line over 3 hours. CDC here and no one knows what’s going on. #coronavirus pic.twitter.com/8nnvUDhRts — Harper ✨ (@drunktweetn) March 14, 2020

Wolf said adjustments weren't made quickly enough, "but we have course corrected."

But the lines are just one of a series of pressure points that have undermined the administration’s efforts to keep the virus from entering the country — and now threaten to hasten its spread:

— The administration’s European travel ban, which President Donald Trump announced Wednesday and went into effect Friday night, sent Americans abroad scrambling to find plane tickets back home. U.S. officials eventually clarified that the ban didn't apply to American citizens or permanent residents — but by then, panic-buying most likely inflated the number of people trying to reenter at once.

— The administration also dramatically narrowed the number of places where air travelers returning from Europe could enter the U.S. — currently just 13 airports. At the same time, Customs and Border Protection and health officials on Friday began doing "enhanced screening" for those passengers, consisting of temperature checks and questions about travel history and symptoms, without having enough staff on hand to process them quickly.

— Customs staffing levels have been inadequate for some time. The union representing Customs screeners said at a hearing in December that the force was short 2,700 officers, partly as a result of the administration’s decision to temporarily reassign people to the U.S.-Mexican border.

— In the early weeks of the outbreak, the administration was slow to ramp up screening at international airports, even for travelers re-entering the United States from known coronavirus hot spots. Harvard public health researchers warned in early March that the screening procedures in place then would miss as many as two-thirds of U.S.-bound passengers entering the U.S.

Now, public health officials are expressing concern that the passengers crammed shoulder-to-shoulder in airport screening lines are at higher risk for catching and then spreading the virus.

“It’s not good public health policy to have crowds of people in tight spaces, especially people who are returning from places where we know there’s widespread transmission occurring,” said John Auerbach, president and CEO of Trust for America’s Health. He added that there should be serious consideration of unintended consequences of the policies being implemented.

With O'Hare among the hardest hit, Illinois leaders blamed the Trump administration for the latest mess, saying it was apparently unprepared to carry out its own orders.

“Appears source of delays all federal and Admin was unprepared after Presidential ban on travel from Europe,” said Illinois Democratic Sen. Dick Durbin on Twitter. The state’s governor, JB Pritzker, wrote: “The federal government needs to get its [email protected]#t together. NOW.”

Durbin and Sen. Tammy Duckworth (D-Ill.) later Sunday jointly called on the administration to direct additional resources to the 13 airports where international passengers from coronavirus-impacted countries are being shunted. They called the response "unacceptable," and noted that the airport hasn't had any contact from DHS, HHS or Customs "to discuss how to accommodate these new travel restrictions, now in effect for travelers coming from 26 additional countries.

Chicago Mayor Lori Lightfoot called on the Trump administration to immediately send more personnel to airports, calling the situation "solely the responsibility of the federal government for not listening."

“When the federal government doesn’t listen and when it doesn’t bring the considerations of mayors and governors and other local officials into the equation, not only are you creating a disaster, not only are you creating a hazardous circumstance that threatens the public, you risk causing serious illness and death," she said at a press conference Sunday.

Acting Homeland Security Secretary Chad Wolf said Saturday that the added screenings are only taking around 60 seconds per passenger. But that doesn’t help if not enough screeners are on duty. And some passengers complained on social media that they waited as long as six or seven hours to be screened.

CBP's acting commissioner, Mark Morgan, said in a statement Sunday that the agency is "working diligently to address the longer than usual delays" and several airports are already improving. A spokesperson was not able to provide details about any specific steps the agency had taken to get lines under control.

"We appreciate the patience of the traveling public as we deal with this unprecedented situation," Morgan said. "We’re continuing to balance our efficiencies with ensuring the health and safety of all American citizens through enhanced medical screening."

Trump noted the long lines in a tweet on Sunday.

"We are doing very precise Medical Screenings at our airports. Pardon the interruptions and delays, we are moving as quickly as possible, but it is very important that we be vigilant and careful. We must get it right. Safety first!" he wrote.

The opposite of social distancing

The thousands of people who have been jammed into close quarters while waiting for their bags and customs checks could be at a greater health risk because of the situation.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said on Fox News Sunday the crowds are “countermanding” the administration’s own mitigation efforts. Public health officials have frequently stressed the importance of social distancing to prevent the spread of the virus.

“What people need to understand is if you're an American is if you're an American citizen, you can get back,” Fauci said. “You don't need to rush back, you will be able to get back but it's understandable how when people see the travel ban, they immediately want to hunker and get home.

“Hopefully we don't have more of that, but I think we probably unfortunately will see that," he said.

Mike Fraser, executive director for the Association of State and Territorial Health Officials, said the large crowds at ports of entry are concerning. | Kathy Willens, File/AP Photo

Mike Fraser, executive director for the Association of State and Territorial Health Officials, said the large crowds at ports of entry are concerning.

“While travel home is essential for these individuals, I would hope federal and airport authorities would work with the airlines and state and local health agencies to practice appropriate infection control measures everywhere, but especially in places were crowds are gathered and recommend staggered arrivals to reduce the number of people congregating in one place, "Fraser said.

“At this time, the goal is to prevent transmission of disease. Any crowded space — churches, grocery stores, airports — all increase the probability of transmission,” said Joyce Johnson, a senior retired U.S. Public Health Service Commissioned Corps officer.

Too little, too late?

These enhanced screenings are also starting too late, following weeks while the virus was already rapidly spreading around the world. The administration’s initial screening efforts focused on travelers from China, even after it had become clear that the virus had spread to other countries.

Marc Lipsitch, head of the Harvard T.H. Chan School of Public Health’s Center for Communicable Disease Dynamics, has said the lax screening of infected travelers may have led to the outbreak in Washington state, the first U.S. state the virus swept through.

Before this weekend, alarmed passengers had reported on social media what they considered lax screening as they returned to the U.S.

Jenn Bartick, a California attorney, told POLITICO that she flew back from Italy two weeks ago and went through “no screening of any type." She said no one asked her if she had been in the parts of Italy that have been hardest hit by the virus, a spread that since prompted Italian authorities to shut down the entire country.

She said when she boarded the plane in Italy, “they asked if I had been to China in the past 14 days. No further screening.” She’s been unable to get a test because she doesn’t have symptoms and is self-quarantining.