EXCLUSIVE: Fresh off a visit to the southern border, Sen. Mike Braun said Saturday that President Biden has a moral imperative to immediately see the "inhumane" and "dangerous" migrant situation firsthand.

The Indiana Republican penned a letter to Biden on Saturday, obtained first by Fox News, which includes pictures Braun took Friday during his visit of a U.S. Customs and Border Protection facility in Texas.

The images show migrants jammed into pods at the processing facility and children sleeping on mats on the floor.

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"The crisis surrounding this surge makes it a moral imperative for you to see firsthand what is happening—and not the sanitized version of the border tour taken by some of my congressional colleagues," Braun wrote. "Having personally gone this week, I can testify to this being an inhumane, unsustainable and dangerous situation.

"You must take swift action before the entire system collapses under its own weight."

Images of migrant children taken Friday, March 26, 2021, at the Donna U.S. Customs and Border Protection (CBP) facility in Texas. Sen. Mike Braun, R-Ind., took the pictures while touring the facility with other GOP senators. (Sen. Mike Braun)

There were more than 18,000 unaccompanied minors in either Border Protection or Health and Human Services custody as of Thursday, according to homeland security records.

By law, children are not supposed to stay in the processing facilities for more than 72 hours before being transferred to HHS shelters specifically designed to care for children. But the surge of migrants at the border has overwhelmed the processing centers and caused delays.

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Biden has said previously he'll visit the border "at some point" though no formal announcement has come on when that might be.

He recently put Vice President Kamala Harris in charge of the White House border response and to work with Central American countries to tackle the root cause of thousands fleeing to the United States. Harris also does not have a trip planned to the border in the near term, her spokesperson told reporters Friday.

Braun was part of a group of Senate Republicans making the trip to the south Texas border and expressed horror at the mounting crisis -- viewing packed border facilities and speaking to overwhelmed border agents.

Border Protection encountered more than 100,000 migrants in February and those numbers are expected to increase dramatically in the spring and summer months. Meanwhile, the administration is scrambling to open new facilities to handle a spike in child migrants -- while calling for federal employees to volunteer to help what the administration concedes are "overwhelming" numbers.

Republicans have blamed the Biden administration for reversing Trump-era policies such as the Migrant Protection Protocols and reviving the policy of releasing migrant families into the U.S. interior.

Images of migrants taken Friday, March 26, 2021, at the Donna U.S. Customs and Border Protection (CBP) facility in Texas. Sen. Mike Braun, R-Ind., took the pictures while touring the facility with other GOP senators. (Sen. Mike Braun)

"An insecure border is not only a humanitarian crisis, but also a dire national security threat," Braun said in his letter to Biden. "I therefore respectfully ask that you take steps to adapt your schedule in order for you to go to the border as soon as possible, and then take steps to halt all incentives to come illegally to our country."

BIDEN MAKES 'NO APOLOGIES' AT NEWS CONFERENCE FOR ENDING TRUMP-ERA MIGRANT PROTOCOLS

During his first press conference as president, Biden made no apologies for rolling back Trump-era immigration protocols, such as the "Remain in Mexico" policy. 

Biden said the vast majority of individuals encountered at the border are being sent back. 

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"First of all, all the policies that were underway were not helping at all, did not slow up the amount of immigration," Biden said. "Rolling back the policies of separating children from their mothers? Make no apology for that.

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"Rolling back the policies of 'Remain in Mexico,' sitting on the edge of the Rio Grande in a muddy circumstance with not enough to eat? I make no apologies for that," Biden said. "I make no apologies for ending programs that did not exist before Trump became president that have an incredibly negative impact on the law -- international law -- as well as on human dignity. And so I make no apologies for that."

Fox News' Adam Shaw and Tyler Olson contributed to this report.