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By Bernd Debusmann Jr
in Washington
Thousands of migrants have been sent from Republican-led states to Democrat-run areas as part of a growing row with the federal government and the Biden administration.
Two buses carrying people primarily from Venezuela were recently left outside Vice-President Kamala Harris' residence in Washington DC. Texas Governor Greg Abbott, who approved the move, then called for tighter immigration policies.
The night before, Florida sent two planes carrying migrants to the wealthy enclave of Martha's Vineyard in Massachusetts, an apparent escalation of a tactic that has also already seen migrants taken to Chicago and New York.
While opponents of the tactic have described it as cruel and inhumane, three state governments insist it is a result of the Biden administration's own border policies.
Why are the migrants being moved?
Three states - Texas, Arizona and Florida - have announced initiatives to move migrants from their states to Democrat-led ones, which they have accused of being "sanctuary" jurisdictions that don't enforce immigration laws.
In an April letter instructing local authorities to begin carrying out the initiative, Governor Abbott argued that the federal government had "no real plan" for addressing an unprecedented "surge of illegal aliens" that might otherwise find themselves in Texan cities.
"Texans cannot continue to shoulder the burdens imposed by open-border advocates in other parts of the country," he wrote.
How many have travelled?
According to statistics compiled by the BBC's US partner CBS, as of 16 September Texas and Arizona had sent almost 300 buses carrying approximately 13,000 migrants to Washington DC, New York and Chicago.
The bulk of these people were sent from Texas, which has spent $12m (£10.5m) to finance the journeys. Arizona has spent about $4m.
While we know Florida's state legislature has appropriated $12m to transport migrants, the exact details of its relocation programme remain unclear.
The BBC has reached out to state officials for comment.
Is bussing migrants legal?
While experts expect that the relocation of migrants will be legally challenged, at the moment it is still unclear what - if any - laws may have been broken. Federal prosecutors and officials are reportedly weighing a range of legal options.
Some - including Chicago Mayor Lori Lightfoot - have suggested that the migrants are being "misled" about the trips. Others have even compared the process to kidnapping and people smuggling.
State officials, however, insist that the migrants are going willingly, and in Texas' case say they have signed a voluntary waiver.
Some of the migrants who arrived in Martha's Vineyard told reporters that they were promised work, assistance and expedited paperwork.
"The big question is what they are being told, and if there is any sort of fraud or inducement," immigration lawyer Aleksander Cuic, the director of the Immigration Clinic at Case Western Reserve University, told the BBC. "But how would anyone know if there's nothing in writing?"
Mr Cuic added that the states will likely argue they are doing a similar thing as the government, which regularly moves detained migrants around the country.
Why are they choosing to go?
According to Adam Isacson, a migration and border expert from the Washington Office on Latin America, many would have ultimately left Texas and the other Republican states anyway.
"You've had migrants coming to all these cities in huge numbers in the past, but they always paid for it themselves," he said. "You've always had tens of thousands of migrants coming to New York City from the border, for example."
Several people who had travelled on these buses told the BBC they were informed of where they were going - and that in some ways, the bus journeys north from Texas was the best available option.
"I could have stayed on the streets [in Texas] or come on the bus. So I came," Darling Vielma, an 18-year-old Venezuelan traveling with two children, said after she was left in Washington DC in early September. "There was nobody for me in Texas."
Similarly, migrants in Texas said they were willing to be transported to other states - and were told where they'd potentially be going - but that officials told them that women and children were being prioritised
Several said they would prefer to be sent out of state than have to remain in Texas, far from family and without shelter.
"I've got to take the opportunity if offered," one man said on Thursday. "Or I'll be out on the street."
What does this mean for US politics?
Mr Isacson described this tactic as "political theatre".
"There are six or seven weeks until the midterms, and Republicans are starting to slip in the polls," he said. "[They] are sort of creating their own [migrant] caravan. It's something that their base can get excited about."
The controversial tactic has already led to an escalating war of words between the White House and the Republican state governors.
President Biden, for example, has accused the governors of "playing politics with human beings" and "using them as props".
The Republicans, in turn, have laid the blame squarely at Mr Biden's feet and derided the Democrats as not doing enough to stop migrants from crossing the border in the first place.
"The minute even a small fraction of what those border towns deal with every day is brought to their front door, they [Democrats] all of a sudden go berserk."
(With additional reporting from Lioman Lima in Washington and Angelica Casas in Texas)