White House officials have tried to pressure US immigration authorities to release migrants detained at the border onto the streets of “sanctuary cities” to retaliate against Donald Trump's political adversaries.

The Washington Post which reviewed emails on the issue and spoke to unnamed officials at the Department of Homeland Security (DHS), said the White House proposed the measure at least twice in the past six months.

According to the emails, the measure was first suggested in November, as a migrant caravan approached the US southern border, and again in February, amid a standoff with Democrats over funding for Mr Trump's border wall.

Sanctuary cities are those where local officials decline to hand over illegal immigrants for deportation.

House Speaker Nancy Pelosi's district in San Francisco was among those the White House wanted to target, according to DHS officials. The administration also considered releasing detainees in other Democratic strongholds.

Migrant caravan reaches Tijuana on US border Show all 30 1 /30 Migrant caravan reaches Tijuana on US border Migrant caravan reaches Tijuana on US border Members of the caravan of Central American migrants climb the border wall in Tijuana, Baja California, Mexico EPA Migrant caravan reaches Tijuana on US border US Border Patrol agents seen through the concertina wire where the border meets the Pacific Ocean AP Migrant caravan reaches Tijuana on US border Central American migrants pray at a temporary shelter in Tijuana AP Migrant caravan reaches Tijuana on US border Darwin, a 12 year old migrant boy from Honduras, looks out from under a tarp while taking refuge at a shelter in Tijuana Reuters Migrant caravan reaches Tijuana on US border Central American migrants line up for a meal at a shelter in Tijuana AP Migrant caravan reaches Tijuana on US border Angel, a 13-year-old migrant from Honduras looks towards the United States past the border fence in Tijuana Reuters Migrant caravan reaches Tijuana on US border Members of the LGBTQ community -who split from a caravan of Central American migrants heading to the US- arrive at the Diversidad Migrante (Migrant Diversity) NGO headquarters, which they will use as shelter, in Tijuana AFP/Getty Migrant caravan reaches Tijuana on US border US military personell install barbed wire fences to stop the passage of Central American migrants EPA Migrant caravan reaches Tijuana on US border Young Honduran migrant Daniel Gamez waits with his family in a line for a meal after arriving with the Central America migrant caravan in Tijuana AP Migrant caravan reaches Tijuana on US border Two women, one carrying a child, walk north after crossing illegally into the United States as a Border Patrol agent moves in to detain them AP Migrant caravan reaches Tijuana on US border epa07165763 People who are part of the first migrant caravan from Honduras start arriving at the border, in Tijuana, Mexico, 14 November 2018. 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EPA/Joebeth Terriquez Joebeth Terriquez EPA Migrant caravan reaches Tijuana on US border A child looks out the window of a bus upon its arrival at a temporary shelter in Tijuana AFP/Getty Migrant caravan reaches Tijuana on US border Migrants from Honduras dry their clothes in the sand after washing off in the Pacific Ocean AP Migrant caravan reaches Tijuana on US border Central American migrants at a temporary shelter near the US-Mexico border AFP/Getty Migrant caravan reaches Tijuana on US border US police agents stand guard near the US-Mexico border fence AFP/Getty Migrant caravan reaches Tijuana on US border A migrant, who claimed not to be part of the Central American migrant caravan walks on the US-Mexico border fence AFP/Getty Migrant caravan reaches Tijuana on US border Eldin, a migrant man from Honduras, awakes next to his seven year old son Jose while taking refuge at a shelter in Tijuana Reuters Migrant caravan reaches Tijuana on US border Migrants line up for food at a shelter AFP/Getty Migrant caravan reaches Tijuana on US border A man installs concertina wire on top of the border structure on the US side AP Migrant caravan reaches Tijuana on US border Central American migrants sit on an overlook in Tijuana AP Migrant caravan reaches Tijuana on US border A migrant, who is part of a caravan traveling en route to the United States, shouts as he waits to receive food in a shelter in Tijuana REUTERS Migrant caravan reaches Tijuana on US border A man tries to get over a border structure topped with concertina wire AP Migrant caravan reaches Tijuana on US border People who are part of the Central American migrants caravan arrive at a shelter EPA Migrant caravan reaches Tijuana on US border A Central American migrant moving towards the United States in hopes of a better life, is pictured next to the U.S. border fence in Playas de Tijuana, Mexico, on November 13, 2018. - US Defence Secretary Jim Mattis said Tuesday he will visit the US-Mexico border, where thousands of active-duty soldiers have been deployed to help border police prepare for the arrival of a "caravan" of migrants. (Photo by Guillermo Arias / AFP)GUILLERMO ARIAS/AFP/Getty Images GUILLERMO ARIAS AFP/Getty Migrant caravan reaches Tijuana on US border epa07174393 Members of the Central American migrant caravan remain at a shelter in the city of Tijuana in Baja California, Mexico, 18 November 2018. The 5,000 member migrant caravan that entered Mexico on 19 October that stopped this week in the city of Tijuana, bordering the US, are expected to meet in this city on the next day to make a decision about their future, according to local authorities. EPA/JOEBETH TERRIQUEZ JOEBETH TERRIQUEZ EPA Migrant caravan reaches Tijuana on US border Migrants pray at a temporary shelter in Tijuana AP Migrant caravan reaches Tijuana on US border Migrants shower outside a temporary migrant shelter next to the Us-Mexico border fence Getty Images Migrant caravan reaches Tijuana on US border US Border Patrol agents, left, speak with two Central American migrants as they sit atop the border structure AP Migrant caravan reaches Tijuana on US border A Central American migrant looks on through the US-Mexico border fence AFP/Getty Images Migrant caravan reaches Tijuana on US border A migrant stands next to the border fence REUTERS

White House officials first broached the plan in an email on 16 November, asking officials at several agencies whether members of the caravan could be arrested at the border and then bused “to small- and mid-sized sanctuary cities”.

The White House told US Immigration and Customs Enforcement that the plan was intended to alleviate a shortage of jail space but also served to send a message to Democrats. The attempt at political retribution raised alarm within the US Customs and Enforcement (ICE), with a top official responding that it was rife with budgetary and liability concerns, and noting that “there are PR risks as well.”

After the White House pressed again in February, ICE's legal department rejected the idea as inappropriate and rebuffed the administration.

A White House official and a spokesman for the DHS sent nearly identical statements to them on Thursday, indicating that the proposal is no longer under consideration.

“This was just a suggestion that was floated and rejected, which ended any further discussion,” the White House statement said.

Ms Pelosi's office criticised the plan.

“The extent of this administration's cynicism and cruelty cannot be overstated,” said Ms Pelosi's spokesperson Ashley Etienne. “Using human beings – including little children – as pawns in their warped game to perpetuate fear and demonise immigrants is despicable.”

Mr Trump has made immigration a central aspect of his administration, and he has grown increasingly frustrated at the influx of migrants from Central America.

He often casts them as killers and criminals who threaten US security, pointing to cases in which immigrants have killed US citizens – including a notable case on a San Francisco pier in 2015. And he has railed against liberal sanctuary city policies, saying they endanger Americans.

“These outrageous sanctuary cities are grave threats to public safety and national security,” Mr Trump said on 7 December in a speech to the Safe Neighbourhoods Conference in Kansas City, Missouri. The speech came less than a month after the White House asked ICE about moving detainees to such cities.

“Each year, sanctuary cities release thousands of known criminal aliens from their custody and right back into the community," Mr Trump said. "So they put them in, and they have them, and they let them go, and it drives you people a little bit crazy, doesn't it, huh?”

Trump shuts down US government over Mexico border wall – in pictures Show all 15 1 /15 Trump shuts down US government over Mexico border wall – in pictures Trump shuts down US government over Mexico border wall – in pictures Federal workers and contractors rally against the partial federal government shutdown Getty Images Trump shuts down US government over Mexico border wall – in pictures The US Capitol on the first morning of a partial government shutdown in Washington EPA Trump shuts down US government over Mexico border wall – in pictures Federal workers and contractors rally against the partial federal government shutdown Getty Trump shuts down US government over Mexico border wall – in pictures President Trump speaks with children who called the North American Aerospace Defense Command Santa tracker in the State Dining Room of the White House. He earlier in the day, tweeted that he was 'all alone in the White House' waiting for Democrats to make a deal on border security EPA Trump shuts down US government over Mexico border wall – in pictures Furloughed federal workers pick up free food at a pop-up store of Kraft Heinz Getty Images Trump shuts down US government over Mexico border wall – in pictures Hundreds of federal workers and contractors rally against the partial federal government shutdown Getty Trump shuts down US government over Mexico border wall – in pictures A pedestrian walk past the U.S. Capitol ahead of a possible partial government shut down in Washington, U.S., December 20, 2018. REUTERS/Joshua Roberts JOSHUA ROBERTS Reuters Trump shuts down US government over Mexico border wall – in pictures From left, House Majority Leader Steny Hoyer, Senate Minority Leader Chuck Schumer, Sen. Dick Durbin and Speaker of the House Nancy Pelosi walk to speak to reporters after meeting with President Donald Trump about border security in the Situation Room of the White House. Trump declared he could keep parts of the government shut down for "months or even years" as he and Democratic leaders failed in a second closed-door meeting to resolve his demand for billions of dollars for a border wall with Mexico Evan Vucci AP Trump shuts down US government over Mexico border wall – in pictures Federal workers and contractors rally against the partial federal government shutdown Getty Images Trump shuts down US government over Mexico border wall – in pictures A sign alerts visitors to the closure of the National Archives on the fifth day of a partial government shutdown EPA Trump shuts down US government over Mexico border wall – in pictures Hundreds of federal workers and contractors rally against the partial federal government shutdown Getty Images Trump shuts down US government over Mexico border wall – in pictures Visitors read signs announcing the closure of the White House Visitor Center EPA Trump shuts down US government over Mexico border wall – in pictures President Donald Trump speaks during a round-table discussion on border security and safe communities with State, local, and community leaders in the Cabinet Room of the White House Getty Images Trump shuts down US government over Mexico border wall – in pictures A sign alerts visitors to the closure of the White House Visitor Center on the first day of a partial government shutdown EPA Trump shuts down US government over Mexico border wall – in pictures Furloughed federal workers show their IDs for entering a pop-up store of Kraft Heinz Getty Images

The White House believed it could punish Democrats – including Ms Pelosi – by busing ICE detainees into their districts before their release, according to two DHS whistleblowers who independently reported the busing plan to Congress.

One of the whistleblowers spoke with The Post, and several DHS officials confirmed the accounts. They spoke on the condition of anonymity to discuss internal deliberations.

Senior Trump adviser Stephen Miller discussed the proposal with ICE, according to two DHS officials. Matthew Albence, who is ICE's acting deputy director, immediately questioned the proposal in November and later circulated the idea within his agency when it resurfaced in February, seeking the legal review that ultimately doomed the proposal.

Mr Miller and Mr Albence declined to comment.

Mr Miller's name did not appear on any of the documents reviewed by The Post. But as White House senior adviser on immigration policy, officials at ICE understood that he was pressing the plan.

Mr Trump has been demanding aggressive action to deal with the surge of migrants, and many of his administration's proposals have been blocked in federal court or, like the family separation policy last year, backfired as public relations disasters.

Homeland Security officials said the sanctuary city request was unnerving, and it underscores the political pressure Mr Trump and Mr Miller have put on ICE and other DHS agencies at a time when the president is furious about the biggest border surge in more than a decade.

“It was basically an idea that Miller wanted that nobody else wanted to carry out,” said one congressional investigator who has spoken to one of the whistleblowers. “What happened here is that Stephen Miller called people at ICE, said if they're going to cut funding you've got to make sure you're releasing people in Pelosi's district and other congressional districts.”

The idea of releasing immigrants into sanctuary cities was not presented to Ronald Vitiello, the agency's acting director, according to one DHS official familiar with the plan.

Last week the White House rescinded Mr Vitiello's nomination to lead ICE, giving no explanation, and Mr Vitiello submitted his resignation on Wednesday, ending his 30-year-career.

Donald Trump declares national emergency to release funds for border wall

Mr Trump told reporters the following day he wanted to put someone “tougher” at ICE.

DHS officials said they do not know whether ICE's refusal to adopt the White House's plan contributed to Mr Vitiello's removal. His departure puts Mr Albence in charge of the agency as of Friday.

The White House proposal reached ICE first in November as a highly publicised migrant caravan was approaching the US. May Davis, deputy assistant to the president and deputy White House policy coordinator, wrote to officials with US Customs and Border Protection, ICE, and the Department of Homeland Security with the subject line: “Sanctuary City Proposal.”

“The idea has been raised by 1-2 principals that, if we are unable to build sufficient temporary housing, that caravan members be bussed to small and mid-sized sanctuary cities,” Ms Davis wrote, seeking responses to its operational and legal viability. “There is NOT a White House decision on this.”

Mr Albence replied that such a plan “would create an unnecessary operational burden” on an already strained organisation and raised concerns about its appropriateness, writing: “Not sure how paying to transport aliens to another location to release them – when they can released on the spot – is a justified expenditure. Not to mention the liability should there be an accident along the way.”

The White House pushed the issue a second time in the midst of the budget standoff in mid-February, according to DHS officials, and on the heels of a bitterly partisan 35-day government shutdown over Trump's border wall plan. The White House discussed the immigrant release idea as a way to punish Democrats standing in the way of funding additional detention beds.

ICE detainees with violent criminal records are not typically released on bond or other “alternatives to detention” while they await a hearing with an immigration judge, but there have been instances of such detainees being released.

The White House urged ICE to channel releases to sanctuary districts, regardless of whether immigrants had any ties to those places.

“It was retaliation, to show them, 'Your lack of cooperation has impacts,' ” said one of the DHS officials, summarising the rationale. “I think they thought it would put pressure on those communities to understand, I guess, a different perspective on why you need more immigration money for detention beds.”

Senior officials at ICE did not take the proposal seriously at first, but as the White House exerted pressure, ICE's legal advisers were asked to weigh in, DHS officials said.

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A formal legal review was never completed, according to two DHS officials familiar with the events, and senior ICE attorneys told Mr Albence and others that the plan was inappropriate and lacked a legal basis.

“If we would have done that, we would have had to expend transportation resources, and make a decision that we're going to use buses, planes, etc. to send these aliens to a place for whatever reason,” a senior DHS official said. “We had to come up with a reason, and we did not have one.”

The proposal faded when House Democrats ultimately relented on their demand for a decrease in the number of detention beds, a final sticking point in budget talks between the White House and House Democrats.

The number of immigrant detainees in ICE custody has approached 50,000 in recent months, an all-time high that has further strained the agency's budget. Those include immigrants arrested in the US interior, as well as recent border-crossers transferred from Border Patrol.

With unauthorised migration at a 12-year-high, the vast majority of recent migrants – and especially those with children – are quickly processed and released with a notice to appear in court, a system that Mr Trump has derided as “catch and release.”

The process has left Mr Trump seething, convinced that immigration officials and the DHS more broadly should adopt a harsher approach.

Mr Vitiello's removal from ICE last week was followed Sunday by the ouster of DHS Secretary Kirstjen Nielsen, who lost favour with Mr Trump and Mr Miller by repeatedly warning the White House that the administration's policy ideas were unworkable and likely to be blocked by federal courts.

The sanctuary city proposal ran contrary to ICE policy guidelines, as well as legal counsel. ICE officials balked at the notion of moving migrants to detention facilities in different areas, insisting that Congress only authorises the agency to deport immigrants, not relocate them internally, according to DHS officials.

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The plan to retaliate against sanctuary cities came just after Mr Trump agreed to reopen the government in late January, following a five-week shutdown over wall funding. The president gave lawmakers three weeks to come up with a plan to secure the border before a second fiscal deadline in mid-February.

During the talks, Republicans and Democrats sparred over the number of detention beds, with House Democrats pressing for a lower number amid pressure from their left flank.

It was during that mid-February standoff that one whistleblower came to Congress alleging that the White House was considering a plan to punish Democrats if they did not relent on ICE funding for beds. A second official independently came forward after that.

According to both, there were at least two versions of the plan being considered. One was to move migrants who were already in ICE detention to the districts of Democratic opponents. The second option was to bus migrants apprehended at the border to sanctuary cities, such as New York, Chicago and San Francisco.