How would Trump’s promise of mass deportations of migrants work?

US President-elect Donald Trump has doubled down on his campaign promise of the mass deportation of illegal immigrants, saying the cost of doing so will not be a deterrent.

In some of his first public remarks since winning the election, Trump said his priority upon taking office in January would be to make the border “strong and powerful".

"It’s not a question of a price tag. It’s not - really, we have no choice," Trump told NBC News.

But how would Trump’s campaign pledge of mass deportations of migrants actually work and what are the hurdles he may face?

The latest figures from the Department of Homeland Security and Pew Research indicate that there are around 11 million undocumented immigrants currently living in the US, a number that has remained relatively stable since 2005.

Most are long-term residents - nearly four-fifths have been in the country for more than a decade.

Immigrants who are in the country without legal status have the right to due process, including a court hearing before their removal. A drastic increase in deportations would likely entail a large expansion in the immigration court system, which has been beset by backlogs.

Most immigrants already in the country enter into the deportation system not through encounters with Immigration and Customs Enforcement (Ice) agents but through local law enforcement.

However, many of the country’s largest cities and counties have passed laws restricting local police co-operation with Ice.

Trump has pledged to take action against these “sanctuary cities”, but America’s patchwork of local, state and federal laws further complicates the picture.

Kathleen Bush-Joseph, a policy analyst at the Washington-based Migration Policy Institute, or MPI, said that co-operation between Ice and local officials would be a "critical" aspect of any mass deportation programme.

"It's much easier for Ice to pick someone up from a jail if local law enforcement co-operates, instead of having to go look for them," she said.

As an example, Ms Bush-Joseph pointed to an early August declaration from the sheriff's offices of Florida's Broward and Palm Beach counties, in which they said they would not deploy deputies to help any mass deportation plan.

"There are many others who would not co-operate with a Trump mass deportation plan," she said. "That makes it so much harder."

Any mass deportation programme is also likely to be almost immediately met with a flurry of legal challenges from immigration and human rights activists.

A 2022 Supreme Court ruling, however, means that courts cannot issue injunctions on immigration enforcement policies - meaning they would continue even as the challenges work their way through the legal system.

Experts estimate that the total bill for one million or more deportations would run into tens or even hundreds of billions of dollars.

The Ice budget for transportation and deportation in 2023 was $420m (£327m). In that year the agency deported slightly more than 140,000 people.

Thousands of immigrants would be detained while awaiting court hearings or deportations, and the Trump campaign has envisioned building large encampments to house them all.

The number of removal flights would also need to be dramatically expanded, possibly requiring military aircraft to augment current capacity.

Just a small expansion in any of these areas could result in significant costs.

"Even a minor change is in the tens of millions, or hundreds of millions," Mr Reichlin-Melnick said. "A significant change is in the tens or hundreds of millions."

Those costs would be in addition to the expense of other border enforcement efforts that Trump has promised: continuing work on a southern US border wall, a naval blockade to prevent fentanyl entering the country, and moving thousands of troops to the border.

Adam Isacson, a migration and border expert from the Washington Office on Latin America, said that "nightmarish images" of mass deportations could also cost a potential Trump administration politically from a public relations standpoint.

"Every community in the US would see people they know and love put on buses," Mr Isacson said.

"You'd have some very painful images on TV of crying children, and families," he added. "All of that is incredibly bad press. It's family separation, but on steroids."

Under the four years of the previous Trump administration, around 1.5 million people were deported, both from the border and the US interior.

The Biden administration - which had deported about 1.1 million people up to February 2024 - is on track to match that, statistics show.

During the two terms of the Obama administration - when Mr Biden was vice-president - more than three million people were deported, leading some immigration reform advocates to dub Barack Obama the "deporter-in-chief".

The only historical comparison to a mass deportation programme came in 1954, when as many as 1.3 million people were deported as part of Operation Wetback, named after a derogatory slur then commonly used against Mexican people.

That figure is disputed by historians, however.

The programme, under President Dwight Eisenhower, ran into considerable public opposition - partly because some US citizens were also deported - as well as a lack of funding. It was largely discontinued by 1955.

Immigration experts say that the earlier operation's focus on Mexican nationals and lack of due process makes it incomparable to what a modern-day mass deportation programme would look like.

"Those [deported in the 1950s] were single, Mexican men," said MPI's Kathleen Bush-Joseph.

"Now, the vast majority of people coming between ports of entry are from places that are not Mexico, or even northern Central America. It makes it so much harder to return them," she added.

"Those are not comparable situations."