WASHINGTON (AP) — Arrests for illegal border crossings from Mexico reached an all-time high in December since monthly numbers have been released, authorities said Friday, exposing a growing vulnerability for President Joe Biden in his campaign for a second term.

The Border Patrol tallied 249,785 arrests on the Mexican border in December, up 31% from 191,112 in November and up 13% from 222,018 in December 2022, the previous all-time high.

Arrests fell more than half during the first two weeks of January, “consistent with historical trends and enhanced enforcement,” U.S. Customs and Border Protection said in a statement. CBP previously said a crackdown by Mexican authorities contributed to the January decline.

Mexicans accounted for 56,236 arrests in December, while Venezuelans were second with 46,937, erasing much of the decline that followed the start of deportation flights to Venezuela in October. Arrests of Guatemalans surged, with Hondurans and Colombians rounding out the top five nationalities.

Tucson, Arizona, was again the busiest corridor for illegal crossings among nine sectors on the Mexican border, with 80,185 arrests. Del Rio, Texas, the focus of Texas Gov. Greg Abbott’s enforcement efforts, was second with 71,095 arrests. San Diego, where nearly 6,000 Chinese were arrested, was a distant third.

When including migrants who were allowed to enter the United States under new or expanded legal pathways, migrant encounters totaled 302,034, topping 300,000 for the first time and shattering the previous high of 269,735 in September. U.S. authorities admitted 45,770 people at land crossings with Mexico in December through an online appointment system called CBP One, bringing the total to more than 413,000 since it was introduced a year ago.

The administration’s broad use of parole authority to allow migrants in the country has been a major sticking point in Senate negotiations over border security.