Declaring illegal immigration a national emergency, Trump ordered the Pentagon to provide support for border wall construction, detention space, and migrant transportation, and empowered the secretary of defence to send troops to the border as needed.
Trump called for his administration to reinstate his "remain in Mexico" program, which forced non-Mexican migrants to wait in Mexico for the resolution of their US cases.
Mexico's National Guard block the advance of migrants to immigration offices in Chiapas. (EPA PHOTO)
Shortly after the inauguration, US border authorities said they had shut down outgoing president Joe Biden's CBP One entry program, which had allowed hundreds of thousands of migrants to enter the US legally by scheduling an appointment on an app. Existing appointments were cancelled, leaving migrants stunned and unsure of what to do.
Trump, a Republican, recaptured the White House after promising to intensify border security and deport record numbers of migrants. He criticised Biden for high levels of illegal immigration during the Democrat's presidency, but as Biden toughened his policies last year and Mexico stepped up enforcement, the number of migrants caught crossing illegally fell dramatically.
Republicans say large-scale deportations are necessary after millions of immigrants crossed illegally during Biden's presidency. There were roughly 11 million immigrants in the US illegally or with a temporary status at the start of 2022, according to a US government estimate, a figure that some analysts now place at 13 million to 14 million.
"As commander-in-chief, I have no higher responsibility than to defend our country from threats and invasions, and that is exactly what I am going to do," Trump said in his inaugural address.
Trump's critics and immigrant advocates say mass deportations could disrupt businesses, split families and cost US taxpayers billions of dollars.
The American Civil Liberties Union said in a federal court filing on Monday that Trump's decision to end the CBP One program removed the only avenue to asylum at the US-Mexico border, an opening salvo by the civil rights group to fight Trump's agenda in court.
In several Mexican border cities, migrants saw their appointments on Biden's CBP One app cancelled just after Trump took office. Some 280,000 people had been logging into the app daily to secure an appointment as of January 7.
Migrants waiting in Ciudad Juarez scrambled to find short-term rentals, buy bus tickets and call family members back home.
Daynna del Valle, a 40-year-old Venezuelan, spent eight months in Mexico waiting for an appointment that would have arrived on Tuesday. In that time, she worked at a nail salon but earned so little that she barely managed to send any money back to her mother in Colombia, a cancer survivor who needed medical treatment for her blood pressure.
"I'm lost," she said. "I don't know what to do, where to go."
In his order focused on so-called "birthright citizenship," Trump called on US agencies to refuse to recognise the citizenship of US-born children without at least one US citizen or permanent resident parent, applying the restrictions in 30 days.
His order prompted the swift filing of a lawsuit in federal court in New Hampshire by the ACLU and other groups, who argued that Trump's order violated the right for anyone born in the United States to be considered a citizen enshrined in the Citizenship Clause of the US Constitution's 14th Amendment.
