For the first time in U.S. history, military aircraft were used this past week to deport scores of undocumented migrants from the United States. Middle schools, Trump administration officials say, are now seen as places to target for immigration enforcement operations. And, according to President Trump's "border czar," every undocumented immigrant should worry they could be arrested at any time, even if they have no criminal record.

The "border czar," Tom Homan, says it's all part of the Trump administration's effort to send a "clear" message: "There's consequences [for] entering the country illegally," he told ABC "This Week" co-anchor Martha Raddatz on Sunday.

"If we don't show there's consequences, you're never going to fix the border problem," he said.

More than 11 million undocumented immigrants are currently estimated to be living in the U.S. President Donald Trump has promised to take unprecedented action to remove as many of them as possible and stem the flow of more migrants coming to the southern border.

In his first several days in office, Trump declared a national emergency at the border, announced an end to the so-called practice of "catch and release" -- when migrants claiming asylum are given court dates and then released pending those proceedings -- and sought to overturn the long-held Constitutional right of birthright citizenship, a move that immediately faced legal challenges and was at least temporarily blocked by a federal judge.

As for the millions of undocumented immigrants already in the country, Homan said the administration will deport "as many as we can," starting with threats to public safety threats and national security, Homan said.

According to estimates released by House Republicans last year, based on government data, hundreds of thousands of undocumented migrants in the country are convicted criminals or have charges pending against them. Government statistics indicate that in the past four years, hundreds of migrants were caught along the southern border with names matching known or suspected terrorists on a government watchlist. And Homan has said more than 2 million people were detected along the border but never captured, so authorities don't know who they are or what threat some of them could pose.

According to statistics released by the Department of Homeland Security last year, a tiny fraction of those who reached U.S. borders in the prior three years had any kind of criminal record, and the vast majority of them involved nonviolent crimes, such as driving under the influence or previously entering the country illegally.

Homan told ABC News that the Trump administration is only "in the beginning stages" of carrying out its mass deportation plan, making public safety threats and national security threats a "priority," but "as that aperture opens, there'll be more arrests nationwide."

And he warned that there will be "collateral arrests," especially in the so-called "sanctuary cities" that he says are resistant to helping Immigration and Customs Enforcement officials locate and arrest undocumented immigrants already in local custody for other crimes.

"Sanctuary cities lock us out of the jails," said Homan, who led ICE as acting director in Trump's first administration.

According to Homan, that creates significant safety concerns: When an undocumented immigrant arrested for a serious crime is released by local authorities, instead of being deported, it "endangers the community."

Nevertheless, Homan said that's a time when ICE officers would likely make "collateral arrests."

"When we find him, he's going to be with others … [and] if they're in the country illegally, they're coming too," he said.

He emphasized that anyone in the country unlawfully is "on the table."

"It's not OK to violate the laws of this country," he said. "We have millions of people standing in line, taking the test, doing their background investigation, paying the fees that want to come in the right way."

"So if you're in the country illegally, you got a problem," he said.

On Monday, during Trump's first day in office, acting Homeland Security Secretary Benjamine Huffman issued a directive telling immigration authorities they could conduct operations in so-called "sensitive" areas that he said were off-limits during the Biden administration.

"Criminals will no longer be able to hide in America's schools and churches to avoid arrest," he said in a statement.

Others, however, said the administration was simply creating fear within the immigrant community, with the chairman of the U.S. Conference of Catholic Bishops' Committee on Migration saying that "turning places of care, healing and solace into places of fear and uncertainty … will not make our communities safer.

He said that as they prioritize national security threats and public safety threats, ICE officers might have to even go into schools because "many" members of gangs tied to South and Central America, such as MS-13, are between 14 and 17 years old.

In his interview with ABC News, Homan said that no other law enforcement agency is restricted from entering certain locations to promote public safety in the same way ICE has been.

"Name another agency, another law enforcement agency, that has those type of requirements, that they can't walk into a school or doctor's office or a medical campus," he said. "No other agency is held to those standards."

"These are well-trained [ICE] officers with a lot of discretion, and when it comes to a sensitive location, there's still going to be supervisory review," he said. "But ICE officers should have discretion to decide if a national security threat or a public safety threat [is] in one of these facilities."

Homan said anyone already in the country unlawfully "should leave," and those looking to claim asylum should "do it the legal way."

"Go to the embassy, go to the point of entry," he said. "You shouldn't come to this country and ask to get asylum and the first thing you do is break our laws by entering illegally."

In the meantime, Homan said the Trump administration is using not just the military but the "whole" government, including the Justice Department, to support its mass deportation plan, which allows ICE officers to concentrate on conducting enforcement operations.

But Homan acknowledged that the federal government won't be able to remove every undocumented immigrant in the U.S., and that his "success is going to be based on what Congress gives us."

ICE doesn't currently have enough funding from Congress to detain all of the undocumented immigrants that the Trump administration says it hopes to arrest.

"I'm being realistic," he said. "We can do what we can with the money we have. We're going to try to be efficient. But with more money we have, the more we can accomplish."

"What price [do] you put on national security?" he added. "When you … don't secure that border, that's when national security threats enter the country. That's when sex trafficking goes up. That's when, you know, that's when the fentanyl comes in."

As for what success practically looks like at the end of the Trump administration, Homan said: "Our success every day is taking a public safety threat off the streets or getting a national security threat out of here."