Migrant encounters along southwest border reach all-time high of 302,000

There were 302,000 encounters along the southwest border in December, marking the highest monthly total ever recorded, sources told ABC News.

Sources stressed the numbers are preliminary and could change.

The numbers -- a hot-button election year topic -- come as the Justice Department threatened to sue the state of Texas over its passage of SB. 4, which allows for state and local law enforcement to apprehend anyone who they believe is in the country illegally.

DOJ says it intends to sue on Wednesday if Texas doesn’t “forbear enforcement of SB 4.”

President Joe Biden “is destroying America,” Texas Gov. Greg Abbott said in response to the threat of a DOJ lawsuit.

“The Biden Admin. not only refuses to enforce current U.S. immigration laws, they now want to stop Texas from enforcing laws against illegal immigration,” Abbott posted on X on Thursday. “I’ve never seen such hostility to the rule of law in America.”

CBP says it has surged personnel to hot spots.

"Encounter numbers continue to fluctuate, as smugglers and bad actors continue to spread falsehoods and show complete disregard for the safety and wellbeing of vulnerable migrants," CBP said in a statement. "We remain vigilant and stand ready to ensure safety of our personnel, migrants, and local communities, and the security of our southwest border."

House Speaker Mike Johnson and other congressional Republicans are headed to the border on the same day the lawsuit is intended to be filed. Homeland Security Secretary Alejandro Mayorkas is set to visit the border next week.

Marsha Espinosa, the former assistant secretary for public affairs at the Department of Homeland Security, said the congressional trip would do less to achieve border security than fulfilling Biden's funding requests.

“While the Biden administration has worked to rebuild the system that Trump demolished, ultimately only Congress can fix this," Espinosa, now a partner at Conexión, said. "It is beyond frustrating that Republicans have ignored or voted against repeated requests for policy changes and funding, which in no doubt contributed to the situation we see today. They don’t need to travel thousands of miles to hold a press conference when all they have to do is walk to the House floor and vote to fund DHS or consider the bill Biden sent them almost three years ago," she said.

Biden sent Secretary of State Antony Blinken and Mayorkas to Mexico last week to meet with the country’s president and their Mexican counterparts as both countries struggle to address urgent issues posed by surging irregular migration.

There are many factors as to why there has been an increase in the number of migrants along the border, experts note.

Smugglers and bad actors driven purely by profit will use anything to drive folks north -- including possible or perceived changes in migration policies (just like they did with Title 42, possible government shutdowns, and other events) -- to prey on vulnerable migrants, a law enforcement source told ABC News.

Additionally, a different law enforcement source told ABC News that the holidays play a factor, and anecdotally, there is misinformation about CBP One app, used by asylum seekers to schedule appointments, shutting down. CBP One, established by DHS to help with the processing of migrants earlier this year, is not shutting down, the source said.

Fake travel agencies emerging in cities like Dakar, Senegal, are also advertising travel to the U.S., according to a CBP official. They advertise visa-free travel to Europe for the Senegalese, which would then open up travel to the Western hemisphere if the offers were legitimate. These “travel agencies” sell complete packages to connect them to a smuggling organization that will then facilitate their movement up to the border, the CBP official said.

The top CBP official said they drop migrants off in remote locations to divert CBP resources.

"These smugglers are recklessly putting migrants into harm’s way: in remote locations across the border, onto the tops of trains, or into the waters of the Rio Grande River," Troy Miller, the acting commissioner of CBP, said in a statement.

A different CBP official said smugglers and bad actors attempt to overwhelm border patrol to "guarantee" release of migrants.

ABC News' Quinn Owen and Alexander Mallin contributed to this report.