It is unclear whether the State Department can redirect all of the money to other parts of the world. Some of the money meant for 2017 fiscal year has already been allocated to specific contracts, so it might not be able to be withdrawn, according to a person familiar with the effort.
Mr. Trump told reporters that he would consider shutting down ports along the border, a decision that could imperil the transit of goods between the United States and Mexico. According to government figures, Mexico is the United States’ third-largest goods trading partner, with $557.6 billion worth of products flowing across the border in both directions.
A move by Mr. Trump to shut down or drastically curb trade with Mexico would pose significant risks to the American economy. It would also represent a stunning reversal in trade relations between the two countries, which last August put their differences aside to renegotiate their portion of the North American Free Trade Agreement. The new deal, known as the United States-Mexico-Canada Agreement, still needs to be approved by Congress.
The president lamented Mexico making a “fortune” off the United States, and said Mexico’s immigration laws were the “strongest immigration laws of anywhere in the world.” (Mexico is much weaker than the United States at enforcing its border laws.) Mr. Trump also again invoked migrant caravans — including one containing hundreds of people heading to the United States — as a reason Mexico needed to act.
“Mexico is tough,” Mr. Trump said. “If they don’t stop them, we’re closing the border.”
Americans would feel the effects in other ways. Border control agencies are already reviewing ways to slow down immigration processing at the border. A senior Homeland Security official confirmed on Friday that shutting down ports of entry along the southwest border is “on the table” to handle the surge in migrants seeking asylum.
Kirstjen Nielsen, the homeland security secretary, said in a statement that she had asked volunteers to add more support at the border, and suggested that American citizens may encounter difficulty getting through as a result.
“Make no mistake: Americans may feel effects from this emergency,” Ms. Nielsen said. “As personnel are reallocated to join the crisis-response effort, there may be commercial delays, higher vehicle wait times at the border and longer pedestrian lines.”