U.S. border agents have confirmed that 1.2 million illegal migrants "got away" from authorities while crossing the border under President Biden's administration, U.S. Customs and Border Protection (CBP) sources told Fox News on Sunday.

CBP tracks hundreds of thousands of migrant encounters at the U.S.-Mexico Border every month, but that stat does not include the number of known "gotaways," or migrants who were detected by authorities but not apprehended. Since Biden entered office in January 2021, border crossings have exploded, and at least 1.2 million migrants successfully evaded authorities.

The first half of Biden's four-year term saw monthly border encounters rise from 101,000 in February 2021 to 251,000 in December 2022, according to CBP stats.

Biden visited the border for the first time in his presidency in early January, but many border agents argued it was too little, too late. The border crisis has drawn even staunch Democrats like New York City Mayor Eric Adams to criticize Biden's handling of the issue.

BIDEN ADMIN FACING THIRD YEAR OF CRISIS AT THE SOUTHERN BORDER WITH UNCERTAIN IMMIGRATION POLICIES IN 2023

Joe Biden southern border immigration

US President Joe Biden speaks with a member of the US Border Patrol as they walk along the US-Mexico border fence in El Paso, Texas, on January 8, 2023.  (JIM WATSON/AFP via Getty Image)

Adams described the border crisis as a national issue last week and called on Biden and Congress to take action. The Northern governor has been dragged into the immigration fight thanks to bussing policies from Texas Gov. Greg Abbott, who has transported thousands of migrants to New York City.

BIDEN-ERA MIGRANT CRISIS SMASHES ANOTHER RECORD AS MIGRANT ENCOUNTERS TOP 250,000 IN DECEMBER

The Republican argues the flow of migrants to powerful Democratic cities like NYC, Chicago and Washington, D.C. is the only way to force Democrats to confront the realities of the border crisis.

Statistics suggest terror organizations are also seeking to take advantage of the border chaos, with terror watchlist apprehensions rising from fewer than 10 annually under former President Donald Trump to 98 in 2022.

Migrants at the El Paso border

More than a thousand migrants awaiting entry into the United States from Juarez, Mexico. (Fox News Digital / Jon Michael Raasch)

US Mexico border security

Vehicles wait to enter the United States Customs and Border Protection (CBP) San Ysidro Port of Entry along the US-Mexico border in Tijuana, Baja California state, Mexico on April 9, 2022.  ((Photo by Patrick T. FALLON / AFP) (Photo by PATRICK T. FALLON/AFP via Getty Images))

The U.S. Customs and Border Protection (CBP) saw an estimated 718,000 border encounters in the first 100 days of fiscal year 2023, which began October 1.

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The White House long sought to dismiss the surge as an annual occurrence, but historical data shows the current crisis is far beyond traditional yearly surges.