U.S. Border Patrol apprehended about 47,000 migrants illegally crossing the southwest border in December, a senior U.S. border official told Reuters. That figure is similar to November's, and well below the Biden administration peak of 250,000 recorded in December 2023. It is also below the 71,000 migrant arrests made in December 2020 as Trump concluded his 2017-2021 presidency.

The number of migrants caught at the northern border with Canada fell to about 500 in December, down from 700 in November, the official said.

Trump, a Republican, returns to the White House on Jan. 20 promising to crack down on illegal immigration and deport immigrants in the U.S. illegally. Republican U.S. Senator Lindsey Graham, a Trump ally, said on Sunday that Trump will need $100 billion for the effort, more than the entire budget of many federal agencies.

The number of migrants caught illegally crossing the border with Mexico rose to record highs during outgoing Democratic President Joe Biden's time in office, but fell dramatically after he toughened his approach last year and as Mexico and Panama stepped up enforcement in the region.

Biden asylum restrictions in June blocked most migrants crossing illegally from claiming asylum and instead encouraged them to use new legal entry programs. The programs include an app known as CBP One that allows migrants in Mexico to schedule an appointment to claim asylum at a legal border crossing and another for certain migrants abroad with U.S. sponsors.

Homeland Security Secretary Alejandro Mayorkas said in a statement that tougher border policies, international cooperation and new legal pathways contributed to "sustained success."

Republicans argue that Biden's legal entry programs overstepped his executive authority. Trump plans to end the programs when he takes office, Reuters reported in November, cutting off pathways that Biden officials say encouraged would-be migrants to enter in an orderly fashion.

Doris Meissner, a senior fellow with the non-partisan Migration Policy Institute, said Biden is poised to hand Trump the most "quiet and stable border" in years, a situation that could change if Trump blows it up without an effective replacement.

"If they simply shut down all of those policies and don't have some other regime to put in place, it could backfire and numbers could go up, because there are a lot of people that are waiting in Mexico," Meissner said.

Trump's transition team spokeswoman Karoline Leavitt criticized high levels of illegal immigration during Biden's presidency and said in a statement that Trump "will use every level of executive and legislative power to secure the border, mass deport illegal criminals, and put American citizens first."

About 280,000 prospective migrants in Mexico have been logging onto the CBP One app daily to try to secure an appointment, a figure that has stayed consistent, according to the senior U.S. border official. The tally includes Mexicans who may be using the app from their homes, the official said.

In both November and December, more migrants were processed through legal border crossings than were caught crossing illegally, according to public and internal U.S. government figures.

Mexico greatly increased its own migration enforcement in the past year amid pressure from the Biden administration.

Trump has taken a combative approach to relations with Mexico and Canada, promising 25% tariffs on all imports until the countries clamp down further on illegal immigration and fentanyl trafficking.

The number of migrant arrests at the U.S.-Mexico border fell sharply in 2020 at the start of the COVID-19 pandemic but then rose later that year, partly due to repeat crossers.