The number of people crossing illegally into the United States from Mexico has dropped by 50 percent in the past month, authorities said on Tuesday, as President Biden comes under growing pressure from both parties over security at the border.
U.S. Customs and Border Protection said it had encountered migrants between ports of entry 124,220 times in January, down from more than 249,000 the previous month.
The figures do not change the fact that the number of people crossing into the United States has reached record levels during the Biden administration, and crossings typically dip in January. Immigration trends are affected by weather patterns and other issues, making it difficult to draw conclusions from monthly numbers.
But the drop in crossings was a glimmer of good news for the Biden administration as House Republicans impeached Alejandro N. Mayorkas, the homeland security secretary, on Tuesday on charges of willfully refusing to enforce border laws. (Their first attempt ended in defeat.)
The figures also amounted to a respite for some large American cities grappling with the burden of sheltering migrants during the wintertime.
In New York City, which is housing more than 65,000 migrants in hotels, shelters and tents, the number of migrants entering the city’s care over the last month plunged to about 1,600 per week, down 55 percent from 3,600 per week in December.
Kayla Mamelak, a spokeswoman for Mayor Eric Adams, said that migrant arrivals in the city correspond directly with border crossings. The number of migrants in city shelters has fallen by 5 percent in the past five weeks, partly because of fewer arrivals and partly because of stricter shelter limits.
Denver, another city struggling with an influx of migrants, received 3,041 in January, fewer than half as many as December’s total of 6,824, according to official data. Only 13 migrants arrived in the city on Feb. 13, compared with 26 on Feb. 12, the data showed.
“If this year’s influx of migrants happens as last year’s, it will come in waves. Those down shifts will be crucial to the city of Denver to get a break, learn how to manage its resources and batten down the hatches for what comes next,” said DJ Summers, director of policy and research at the Common Sense Institute in Denver.
Many of the migrants arrived in Democratic-led cities like Boston, Denver, Chicago and New York after traveling on buses sent by Gov. Greg Abbott of Texas, who argues that cities far from the border should share the burden of migrants in his state. Democratic mayors have accused him of using human beings as props.
Troy A. Miller, the acting head of the border agency, said the drop in border crossings is the result of “seasonal trends, as well as enhanced enforcement efforts” by Border Patrol and “our international partners.”
In late December, Mr. Biden sent Secretary of State Antony J. Blinken and other top American officials to Mexico City, where they met with President Andrés Manuel López Obrador to find a way to slow the surge in illegal crossings.
Since that meeting, Mexico has been intercepting some migrants traveling north to the United States, according to Jennifer Piper, program director for the American Friends Service Committee, a Quaker organization that operates in Mexico.
The United States has also stepped up pressure on countries like Panama and Guatemala to take measures to prevent migrants from advancing toward Mexico.
Adam Isacson of the Washington Office on Latin America, a human rights organization, said the dip in numbers was likely connected to a few factors. Among them were rumors that U.S. officials were going to close the border in December; another was Mexico’s stepped-up enforcement, including by taking migrants off trains headed to the southern border and boosting checkpoints.
Mr. Isacson also noted that border crossing numbers regularly fall from December to January.
“It seems to be a combination of weather (rainy in the south, bitter cold at night at the border), plus people don’t like to leave home during the end-of-year holidays unless they have absolutely no choice,” he said.
Immigration has taken on enormous political importance as this year’s presidential election approaches. Mr. Biden has blamed his predecessor and putative challenger, former President Donald J. Trump, for undermining a bipartisan immigration deal in Congress that would crack down at the border.
And immigration experts say they expect another rise in numbers soon.
Casa Alitas, a Catholic agency that runs several shelters in Tucson, said numbers have been steadily climbing again.
In October, November and December, the shelter network was receiving about 1,000 migrants each day. That number plummeted to an average of about 500 daily in the first three weeks of January. This week, numbers were in the 1,000 range again.
Diego Piña Lopez, the agency’s director, said the numbers had gone up “slowly but surely.”
Andy Newman and Luis Ferré-Sadurní contributed reporting from New York.
