The government shutdown is now the longest in U.S. history, now on its 35th day after a 14th failed vote in the Senate to end it.

Some in Congress are signaling that enough is enough, hinting that a deal could be coming to reopen the government. Until a deal is reached, there are fears the travel impact could get worse.

Closing airspace is what the Secretary of Transportation Sean Duffy said is a possibility if they don't reach an agreement soon. Aviation experts said that would be an unprecedented step, but it's one they might have to take if air traffic controllers don't get paid or show up to work.

Travelers at O'Hare International Airport on Monday were met with clear security lines and few delays, but there still is plenty of anxiety for flyers like exchange student Basia Kaminska due to the government shutdown.

"Always anxious," said Liz Brown-Reeves, who was dropping her off. "She's 16 years old, so just nervous about dropping her off. You know, once you take her across the line to the departing flight, hopefully everything is on time."

"I was at the line for like about five hours, but I still didn't get to the check-in," said one traveler heading to Phoenix.

So far, three million Americans have been met with delays and cancellations. People at Phoenix airports are also waiting in long TSA lines.

"I've been here for four hours. My feet hurt, my legs hurt, my back hurts. I'm very tired," Salma Amoud said. 

In Houston, TSA agents were only able to staff two of the five terminals because of low staffing due to sick calls and no recent paycheck — putting a strain on the system.

"Many of the controllers said, a lot of us can navigate missing one paycheck. Not everybody, but a lot of us can. None of us can manage missing two paychecks," Duffy said.

Duffy said this week, controllers and TSA agents will miss another paycheck. He also said 46% of Monday's flight delays were due to the government shutdown and fears more are coming.

"So, if you bring us to a week from today, democrats, you will see mass chaos. You will see mass flight delays, you'll see mass cancellations, and you may see us close certain parts of the airspace because we just cannot manage it," he said.

DePaul University transportation expert Joe Schwieterman said with Thanksgiving coming in the next few weeks, it's going to be a pivotal time, and people flying may want to start preparing for long delays.

"When you throw on delays in that environment, airlines can't respond as well, and I think that's the concern leading up to that, and it's going to put us in uncharted waters," Schwieterman said.

Duffy said if the government does reopen soon, he is confident they will recover, and air traffic controllers and TSA agents will come back to work quickly.