Gen. James “Mad Dog” Mattis, the US defense secretary, defended the Trump administration’s deployment of nearly 6,000 active duty US troops to the US border with Mexico to turn back refugees as a “moral and ethical mission” as well as good training for deployment to wars abroad.

The Pentagon chief spoke Wednesday as he traveled to south Texas to review some of the active duty US troops who have been sent to the border with Mexico to block the entry of refugees and migrants fleeing conditions of repression, violence and grinding poverty in Central America.

Accompanying Mattis was Department of Homeland Security Secretary Kirstjen Nielsen, who, according to a Washington Post report is about to be fired from her post because of the belief on the part of Trump and some of his right-wing aides that she has been insufficiently ruthless in the implementation of the administration’s anti-immigrant measures.

The visit coincided with the arrival at the US border of the first contingent from the main caravan that departed from Honduras on October 13. Nearly 400 Central American migrants reached Tijuana on Tuesday aboard nine buses. They were preceded by a smaller group of some 80 LGBT migrants who reached the border city two days earlier.

Some of the migrants marched to the steel border fence that reaches out into the Pacific Ocean, with a few of them scaling it and chanting “Trump, build a bigger wall.” Others waved a Honduran flag and chanted “Sí se pudo!” or “Yes we could.”

Three youth, one of them 17 years old, jumped off the wall onto US territory, confronting a phalanx of Border Patrol agents backed by vehicles and a helicopter. Picking up trash on the beach, one of the youth shouted to the agents, “We’re doing something good. We can do this, right? Clean up your country,” the Mexican daily Reforma reported. They then jumped back over to the Mexican side.

The bulk of the migrants traveling in caravans—self-organized groups of men, women and children who have banded together for reasons of solidarity and security as they make the perilous trip through Mexico—are still over 1,000 miles away from the US border. Some are moving northward through the Mexican state of Sinaloa along the Pacific Coast route toward Tijuana. Approximately 1,300 are resting in a Mexico City sports stadium, with plans to get back on the road on Friday.

The trip by Mattis and Nielsen was aimed at defending and legitimizing Trump’s decision to deploy regular Army troops to the border, an action that flies in the face of posse comitatus, which bars the military from performing domestic police actions, and which militarizes the US response to refugees, raising the prospect for a massacre on the border.

The deployment of the troops was ordered in the context of midterm elections, in which Trump toured the country declaring before rallies that the approach of the Central American migrants and refugees constituted an “invasion,” while casting the men, women and children fleeing northward as cutthroats and criminals. While stoking racism and xenophobia on this issue continuously in the run-up to the election, in the wake of the vote, Trump has fallen silent on question, making it clear that from the start he had demagogically exploited the migrants to advance his reactionary political agenda.

Democrats, meanwhile, have completely accommodated themselves to this anti-immigrant tirade, with the party’s leadership insisting that candidates avoid the issue of immigration, giving a free rein to the Trump administration to implement its repressive and illegal measures.

These have included not only the troop deployment, but also the radical restriction of the right to asylum in violation of both international and US law, subjecting those seeking asylum after crossing the border without presenting their papers to US authorities to summary deportation. The aim is to force refugees to report to US ports of entry, where they are being forced to wait for weeks to apply, many are unlawfully turned away and those who make it across are subjected to detention and likely denial of asylum. With the so-called “hardening” of these ports of entry by the US military, the process has become even slower and fraught with new dangers.

Thus far, the US troops have been engaged in stringing concertina wire and erecting barricades at border crossings, a task that Mattis indicated would be completed within the next week to 10 days.

Reports indicate that the morale among the American soldiers is low. They are living in tent camps without electricity or dining facilities and eating MREs, under conditions that some have compared to the early days of the US invasion of Afghanistan. Moreover, many are conscious of the dubious legality and reactionary nature of their “mission.”

In his trip to the US military camp near McAllen, Texas, General Mattis brushed aside questions as to the legality and rationality of the military deployment on the border, describing the massive show of force against unarmed refugees as a “moral and ethical mission.”

One of the soldiers he met with asked him what the short- and long-term plans were for the border deployment. He answered that the short-term plan was to complete the laying of barbed wire and other barricades. As for the long-term plan, he declared that it was “somewhat to be determined.”

“When you’re in something like this,” Mattis said, “it’s dynamic, it’s unpredictable. We’ll have to see” what happens when the Central American immigrants arrive at the border.

Despite Pentagon claims that US troops will not come into direct contact with the immigrants, Mattis’ statements held open the prospect that their mission could easily change, including into providing lethal support for border agents. CNN reported Wednesday that the Pentagon had asked the Department of Homeland Security to request additional authorization from the White House to use the military in direct policing of the border, in direct violation of posse comitatus.

Mattis spelled out the threatening character of the deployment by placing it in the context of earlier acts of US military aggression.

“I would put this in a little historic context,” Mattis said. “President Wilson 100 years ago… deployed the US Army to the southwest border… The threat then was Pancho Villa’s troops, a revolutionary raiding across the border into the United States: New Mexico in 1916.”

This invocation of the punitive expedition led by Gen. John Pershing in the unsuccessful pursuit of Pancho Villa inside Mexico underscores the aggressive character of the US deployment on the border. Within Mexico, with its long history of US imperialist aggression, from the bloody war launched in 1846 that robbed the country of half its national territory, through to the multiple interventions carried out during the Mexican Revolution between 1914 and 1917, Mattis’ words will no doubt be read as a direct threat.

The Pentagon chief also said that the deployment on the border was “very good training” for wars abroad. “In terms of readiness, it’s actually, I believe, so far improving our readiness for deployments,” he said.

It is also, obviously, “very good training” for the deployment of the US military on US soil to suppress working class unrest. While aimed today against immigrants forced from their countries by the desperate conditions created by decades of imperialist oppression, US-backed dictatorships and CIA-orchestrated coups, tomorrow it can be directed against the rising tide of class struggle within the American working class as a whole.

This threat can only be met by the struggle to unite the working class across national boundaries and the defense of the rights of asylum seekers and immigrants to live and work in the US with full legal and citizenship rights, free from fear of deportation and repression.