Homeland security secretary Kirstjen Nielsen has asked other federal departments to send civilian police to the border in order to deal with migrant caravans making their way to the U.S.

The memo, obtained by Politico, highlights the continuing crisis over a number of caravans that have originated in Central America and are making their way through Mexico to the U.S. border.

The request suggests that personnel with such assignments as guarding diplomats, patrolling national parks, and protecting nuclear weapons might effectively "become Customs and Border Protection personnel," as one former Justice Department official put it, with the power to arrest border-crossers.

Although the White House position on the request is unclear, such an action would be the latest extraordinary Trump administration effort to crack down on border security amid what President Donald Trump has increasingly cast as an immigration crisis.  In particular, Trump has recently depicted a northbound migrant caravan as an attempted "invasion" of the U.S.  But there is little evidence that existing border officials are unable to prevent members of the caravan, currently marooned in Mexico, from entering the country.

A senior DHS official who confirmed the memo's authenticity said the Justice Department has already made a commitment to dispatch officers to the border, and that DHS is actively "working with" other departments named in the memo to determine the availability of law enforcement resources.

Is this an admission that the situation may get out of control?  An unknown number – publicly anyway – of caravans are on their way to the U.S., with potentially thousands of people who want asylum.  This is the Mariel Boat Lift in slow motion, where Fidel Castro allowed tens of thousands of Cubans to emigrate to the U.S. at once.  The resulting chaos was exactly what Castro wanted, as President Carter appeared paralyzed to do anything about it.

The president has decided that asylum-seekers will wait in line to be processed and will be denied the opportunity to flee the border for the interior of the country.  But Mexico is going to have none of this.  The Mexicans will insist that the asylum-seekers wait on the U.S. side of the border.  There are potentially tens of thousands of asylum seekers who may be on their way here.  The Border Patrol is going to need a lot more help to keep the situation from getting out of control.

This is a prudent move by Nielsen, but a troubling one as well.  The mayor of Tijuana has called for the arrest of the organizers of these caravans, which is a good idea but probably won't happen.  As long as these open borders fanatics are sending the caravans northward, there is going to be a crisis.