Transportation Secretary Sean Duffy on Sunday declined to apologize for the nationwide ground stop on Friday that stranded hundreds of thousands of travelers across the country following a router issue that derailed air traffic control communications.

Instead, the secretary blamed his predecessors and previous presidential administrations that he said did not do enough to modernize the nation’s air traffic control system.

“It happened on my watch, but we have to be clear: I am moving at an incredible speed that no one has done at the FAA or in decades, and I’m proud of the work we’re doing, the attention we’re bringing to this issue,” Duffy told NBC News’ “Meet the Press.” “But I can’t apologize for what was passed off to us, and I can’t blame Republicans or Democrats because it’s all of them.”

The secretary also blamed “30 years of a lack of investment,” from the country’s previous leaders.

“Why they didn’t do that I don’t know, but they gave me a system that needs to be fixed, and President [Donald] Trump and I are going to fix it,” he added.

His remarks come less than two days after the Federal Aviation Administration issued a national ground stop that lasted several hours, leading to thousands of flight cancellations beginning on Friday and continuing through the weekend.

FAA contractor L3Harris was working on replacing a copper line with a fiber line at a remote site when the work led a router to overwhelm the national FAA telecommunications network, Duffy said Saturday.

Duffy also said Sunday on “Meet the Press” that he expects airports and airlines to resume normal operations by the end of the day or early Monday morning.

“By the end of today, into tomorrow, I think we’ll be back to normal,” he said, adding that Friday’s ground stop led airplanes and flight crews to be “out of position.”

“It takes some time for the airlines to rechoreograph all of their crews and aircraft. We’re going to start seeing things get better today, but I think back to normal tomorrow,” Duffy said.

The secretary also demurred when asked whether he could guarantee that a similar travel disruption won’t happen in the future.

“First we have to figure out what happened. Was this a faulty installation by L3Harris that was doing their work for us? Was it a fault of the router itself? We have to do that investigation and make sure we take precautions. We don’t want to shut down the airspace,” Duffy told “Meet the Press” moderator Kristen Welker.

“We’re going to figure out what was the root cause and then move forward from there, fixing how we do business at the FAA,” he added.

Duffy also reiterated a call he’s made all weekend for more funding from Congress to modernize the nationwide air traffic control system, which has long been outdated and faced problems.

“The president, since he came to office, has been pushing for modernization of the airspace. Before I was even sworn in, he brought this up,” the secretary said, pointing to $12.5 billion that was allocated for air traffic control improvements in a GOP-backed spending bill last year.

“The Congress was very specific in how I spend that money. I have a certain allotment for radar, a certain allotment for radios, a certain allotment for building new infrastructure for my centers for air traffic controllers. They didn’t give me money for telecom. They didn’t give me money for new software,” Duffy said.

“I’m coming back to Congress and the American people to explain all the great work we’re doing right now,” he continued. “We’re going to spend that $12.5 billion by the end of 2028, but I need the rest of the money for software and a new telecom architecture that will be way more resilient. I need that money so I can start that build.”

On Saturday, NBC News reported that on Thursday, just one day before the ground stop, Duffy and Office of Management and Budget Director Russell Vought sent a letter to members of Congress asking lawmakers for $30.1 billion to upgrade the United States’ aging airports and air traffic control system.

They wrote: “This investment is critical to complete the modernization of our national airspace — delivering a resilient telecommunications backbone for air traffic controllers, modern hardware and software, state-of-the-art control towers, and world-class airport infrastructure. These investments will address current challenges, including weather-related delays, while preparing the National Airspace System for emerging demands, such as safely integrating air traffic with the growing space industry.”

On Sunday, Duffy urged Congress to “just do it.”

“I’m doing all I can to keep people safe,” he said. “But I’m also telling you, if you don’t give us the resources, we can’t complete the job. And this is — of all the partisanship — this is the most bipartisan thing in all of Washington. Democrats, Republicans, the president, everyone agrees on this. Let’s just do it.”