Former President Donald Trump has vowed, if he's elected, to conduct a large-scale deportation operation that some immigration and military experts agree is theoretically possible but also problematic, and could cost tens -- even hundreds -- of billions a year.

In FY 2023, Immigration and Customs Enforcement (ICE) officers conducted 170,590 administrative arrests, representing a 19.5% increase over the previous year, and more than any year of the Trump presidency.

Should he win a second term, Trump has promised to exponentially increase this work and suggested deporting all of the estimated 11 million people living in this country without legal immigration status.

His team, at various points, has suggested starting with "criminals," though they have provided few specifics about who would be prioritized.

One cost estimate: $88B - $315B a year

A new report from the American Immigration Council, an immigration rights research and policy firm, estimates that to deport even one million undocumented immigrants a year would cost over $88 billion dollars annually, for a total of $967.9 billion over more than ten years.

The report acknowledges there are significant cost variables depending on how such an operation would be conducted and says its estimate does not take into account the loss of tax revenue from workers nor the bigger economic loss if people self-deport and American businesses lose labor.

A one-time effort to deport even more people in one year annually could cost around $315 billion, the report estimates, including about $167 billion to detain immigrants en masse.

The two largest costs, according to the group, would be hiring additional personal to carry out deportation raids and constructing and staffing mass detention centers. "There would be no way to accomplish this mission without mass detention as an interim step," the report reads.

Trump campaign official agree one of the biggest logistical hurdles in any mass deportation effort would be constructing and staffing new detention centers as an interim solution.

Stephen Miller, a senior adviser to Trump, has repeatedly said that should Trump win the White House, his team plans to construct facilities to hold between 50,000 – 70,000 people. By comparison, the entire U.S. prison and jail population in 2022, comprising every person held in local, county, state, and federal prisons and jails, is currently 1.9 million people

The American Immigration Council report estimates that to deport one million immigrants a year would require the United States to "build and maintain 24 times more ICE detention capacity than currently exists."

There are currently an estimated 1.1 million undocumented immigrants in the country who have received "final orders of removal." Those individuals, in theory, could be removed immediately by ICE agents, but because of limited resources ICE agents have instead focused lately on those people who have recently arrived or who have dangerous crimes

"I think it is possible that they could execute on this. The human resources would be the hardest for them to overcome. They would have to pull ICE agents from the border if they want to go into cities," Katie Tobin, a scholar at the Carnegie Endowment for International Peace who served as President Joe Biden's top migration adviser in the National Security Council, told ABC News.

ICE agents currently help Customs and Border Patrol agents on the border, carrying out expedited deportations of new arrivals who have recently crossed into the country illegally and provide logistical support to the Department of Homeland Security.

A new mandate to round up and deport individuals who have been living in the country for some time could mark a significant change for the law enforcement agency.

The American Immigration Council report estimates that to carry out even one million deportations a year, ICE would need to hire around 30,000 new officers, "instantly making it the largest law enforcement agency in the federal government," the report reads.

Trump campaign: Deportation cost less than migrant costs

The Trump campaign has argued the cost of deportation "pales in comparison" to other costs associated housing and providing social services to recent migrants. "Kamala's border invasion is unsustainable and is already tearing apart the fabric of our society. Mass deportations of illegal immigrant criminals, and restoring an orderly immigration system, are the only way to solve this crisis," Karoline Leavitt, national press secretary for Trump's campaign, told ABC News in a statement.

Trump has promised to mobilize and federalize National Guard units to help with the deportation effort, which would likely be a first for the military.

Under U.S. law, military units are barred from engaging in domestic law enforcement, although Trump has proposed invoking the Insurrection Act, a sweeping law, that could give him broader powers to direct National Guard units as he sees fit.

"We don't like uniform military in our domestic affairs at all," William Banks, professor at Syracuse University and Founding Director of the Institute on National Security and Counter Terrorism, told ABC News in a phone interview. "The default is always have the civilians do it. The cops, the state police, the city police, the sheriffs," he went on.

Using the military for domestic law enforcement would be a fundamental shift, one which Banks argues too few Americans have considered or grappled with.

"It would turn out whole society upside down … all these arguments about him being an autocrat or dictator, it is not a stretch," he said. For example, uniformed military officers are not trained in law enforcement and if they were asked to conduct civilian arrests there could be significant civil liberties conflicts and violations.

In order to, target and deport immigrants whose have not received "final orders of removal" but whose cases are still pending, Trump has discussed using another rare legal maneuver to himself broad authority to target and detain immigrants without a hearing, specifically invoking the Alien Enemies Act of 1798, a wartime law last used during World War II to detain Japanese Americans.

Trump would also need other nations to accept deported individuals and allow deportation flights to land back on their soil.

Katie Tobin, a scholar at the Carnegie Endowment for International Peace who served as President Joe Biden's top migration adviser on the National Security Council, told ABC News, “Last time the Trump administration did not hesitate to threaten punitive action to countries that didn’t cooperate with them on immigration, but there are some practical issues there in terms of just how many flights a country like Guatemala or Colombia can accept per week.”

There would likely be less tangible and more indirect costs of a mass deportation effort as well. Inevitably there would be ripple effects throughout the economy. In 2022 alone, undocumented immigrant households paid $46.8 billion in federal taxes and $29.3 billion in state and local taxes, according to the report, and "undocumented immigrants also contributed $22.6 billion to Social Security and $5.7 billion to Medicare."

The human toll

Experts also predict that if a future Trump administration were to follow through with some large, initial and highly visible deportation operation, a significant number of individuals and families would likely choose to self-deport in order to avoid family separations or having to spend time in a military-style detention center.

The authors of the American Immigration Council report argue that the effect of a mass deportation program, as described by Trump and his advisers, would "almost certainly threaten the well-being" of even those immigrants with lawful status in the United States and "even, potentially, naturalized U.S. citizens and their communities."

"They would live under the shadow of weaponized enforcement as the U.S. went after their neighbors, and, as social scientists found under the Trump administration, would be prone to worry they and their children might be next," the report says.

In recent interviews and conversations with reporters, Trump's running mate Ohio Sen. JD Vance has dodged the question of whether a future Trump administration would separate families during a new deportation effort or in detention centers along the border.

"If a guy commits gun violence and is taken to prison, that's family separation, which, of course, is tragic for the children, but you've got to prosecute criminals, and you have to enforce the law," Vance told reporters in September when visiting the border.