The US military is to be deployed to the border with Mexico, it was reported on Thursday, with James Mattis, the defense secretary, poised to sign deployment orders sending 800 troops to the region.
The move is being seen as a response to a "caravan" of 7,000 Central American migrants, which is edging its way north through Mexico, with the intention of crossing into the US and claiming asylum.
Donald Trump, the US president, is obsessed with the caravan, seeing it as catnip for his core voters ahead of the November 6 midterms.
On Thursday morning he tweeted that he was "bringing out the military" to address what he's calling a national emergency at the southern border.
Border crossings this spring were at a 40-year low. Around 300,000 people have crossed this year - well down from the early 2000s, when over a million crossed the border annually.
Mr Trump on Wednesday evening told a rally in Wisconsin that the military was "all set."
Mr Mattis is now believed to be finalising details of where the troops will come from, where they will be deployed, and what their role will be.
The troops will not engage in lethal operations to stop the migrants, CNN reported.
Instead they are expected to provide fencing, wall materials and other technical support at several key points along the border where it is believed the migrants may try to cross.
In this their role will be similar to that of the national guard, which was deployed in April and helps with manual labour. There are 2,200 national guard troops now serving on the border; 1,145 soldiers in Texas, 115 in New Mexico, 580 in Arizona and the remaining 360 in California.
The troops sent by Mr Mattis will also provide tents and medical care for border authorities in those areas.
They retain the right of self-defence, but border patrol officers will still be the ones physically stopping illegal migration.
It is not yet clear if all or part of the new deployment will be federally-activated national guard forces - those currently there were sent by individual states, in response to the April announcement - or active duty troops.
The troops are expected to be in position next week in advance of a possible arrival of some of the caravan.