Venezuelan migrants were recently sent from Texas to just outside Vice-President Kamala Harris' residence
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 to Democrat-led ones, which they have accused of being "sanctuary" jurisdictions that fail to enforce immigration laws.
Officials in those states say the tactic is aimed at mitigating the impact of migration flows in local communities.
They have also said the measure is designed to increase pressure on the Biden administration to do more to reduce the number of people crossing the US-Mexico border, which has hit a record high this year.
In a 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.