As a major storm heads for Puerto Rico, the Department of Homeland Security and its Federal Emergency Management Agency said Tuesday they will move $271 million in funds to support President Trump's border enforcement efforts.

The Department of Homeland Security said it will transfer the emergency funds — including $155 million from FEMA's disaster relief fund — to support new Immigration and Customs Enforcement detention beds as well as facilities for related court cases, according to documents obtained by NPR.

In a July notification to Congress about the transfer, DHS said the $155 million comes from recoveries of prior year funds and that "absent significant new catastrophic events" the department believes the fund will still have enough money to operate.

Congressional Democrats slammed the move on Tuesday, which comes at the peak of hurricane season and as Tropical Storm Dorian was poised to reach hurricane levels.

"The Trump administration's plan to divert money away from FEMA at the start of hurricane season to continue its efforts to separate and jail migrant families is backwards and cruel," Senate Minority Leader Chuck Schumer, D-N.Y., said. "Taking these critical funds from disaster preparedness and recovery efforts threatens lives and weakens the government's ability to help Americans in the wake of natural disasters. Congress appropriated these funds to meet the American peoples' priorities and I strongly oppose this effort to undermine our constitutional authority."

DHS alerted Congress to the move in a 15-page notification dated July 26, which NBC first reported earlier Tuesday. The agency is required to give Congress a 30-day notice to the plans.

Democrats, opposed to the move, waited to respond until the end of that notification period in hopes of delaying the costly action, a congressional source familiar with the plans said.

"I have significant concerns about the intended use of funds, and consequently, about the tradeoffs between that use and activities that would otherwise be funded from the source accounts," California Rep. Lucille Roybal-Allard, chair of a House Appropriations subcommittee, told DHS Secretary Kevin McAleenan in an Aug. 23 letter.

Roybal-Allard said the the reprogramming was unnecessary and the Trump administration was overstepping its authority. She noted that DHS components such as the U.S. Coast Guard could be hampered by the move.

She added she was concerned about implementation of the agency's immigration enforcement operations, which often ignores its budget directives from Congress and lack transparency. She urged McAleenan to work with the House Appropriations Committee to restore their partnership.

"I am greatly concerned that during the course of this administration, there has been a growing disconnect between the will of Congress, as represented by ICE funding levels in enacted appropriations bills signed by the President, and the Department's Immigration enforcement operations, which often lack justification," Roybal-Allard said.

Sen. Jeff Merkley, D-Ore., also slammed the move Tuesday.

"Once again, this administration is endangering America by moving funds away from emergency management for their extremist border agenda," he said. "President Trump and his administration are not just endangering the lives of the children and families they seek to harm in the name of deterrence. By shortchanging preparedness, they're endangering the lives of millions of Americans who live in hurricane zones as well."

The DHS notification to Congress expired on Sunday, the agency said in a statement Tuesday. The Department also defended the move, saying it is necessary to deal with the influx of migrants.

"Given the rise of single adults crossing the border, ICE has already had to increase the number of detention beds above what Congress funded," DHS said in its statement. "Without additional funding for single adult detention beds and transportation from the U.S. Border Patrol to ICE detention facilities, ICE will not be able to support the influx of migrants from U.S. Customs and Border Protection apprehensions."

In its notification, DHS cited "a security and humanitarian crisis on the southern border" and the "high volume of aliens presenting themselves at ports of entry or entering illegally ... and being released into the interior of the United States while they wait sometimes years for a final resolution of their case." The shift in the funds would help DHS address the "crisis," the department says, under authority provided in the fiscal year 2019 DHS appropriations act.

As a result, DHS said it will transfer funds from its FEMA disaster relief fund and other accounts to the new border effort.

Of the overall $271 million total, the agency said it will move $155 million to establish and operate temporary Migrant Protection Protocol, or MPP, Immigration Hearing Facilities along the Southwest border. Another $116 million will be used to pay for new detention beds, the agency said.

"MPP court docket backlogs will continue to grow and ICE will not be able to effectively and efficiently move single adult migrants between detention centers and courtrooms without the funding," the agency said. "This realignment of resources allows DHS to address ongoing border emergency crisis by alleviating the surge along the Nation's Southwest Border while minimizing the risk to overall DHS mission performance."

Supporters of the administration's immigration policies say Democrats have left the administration little choice but to take this action.

Jessica Vaughan, director of policy studies for the Center for Immigration Studies, who is in regular discussions with the administration, said the transfer of the funds is necessary because ICE is so over budget due to the border crisis. They have to find the money from somewhere because Congress hasn't given them what it needs, she said.

"ICE's priority caseload is growing, but the Democratic majority in the House does not support the level of enforcement that they consider to be the bare minimum for public safety and maintaining the most basic integrity of the law," she said.

"The border influx has strained ICE capacity," she said. "Under the law, their detention capacity is set by Congress. They have to balance the criminal cases, border cases and other priorities like worksite operations and fugitives. And on top of that some people are mandatory to detained, such aggravated felons and prior deportees."

Franco Ordoñez contributed to this report.

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