The Pentagon offered new details Monday about the types of activities National Guard troops would perform while deployed by President Trump to the U.S. -Mexico border, but critical questions remain about how long the operation will last and how much it will cost.
The troop deployment appeared to catch military and Homeland Security officials by surprise last week, as Trump fumed at Mexico over reports that a caravan of more than 1,000 Central American migrants was en route to the US border.
California and New Mexico, the two other states bordering Mexico, have not made public commitments to sending Guard members.
Texas officials showed images over the weekend of guard members arriving at the border but the state's National Guard did not respond to queries Monday about how numerous 250 troops it said would be at the border soon had arrived. On Monday, Arizona Gov. Doug Ducey, responding to the executive order Trump signed last week, sent 225 Arizona National Guard personnel to the Tucson and Yuma Border Patrol sectors.
Brown has repeatedly fought with Trump over immigration policy.
Apprehensions are still well below their historical trends during the terms of former Presidents George W. Bush and Barack Obama, both of whom also deployed the Guard to the border. That's about double the number of US troops deployed to Syria.
The statement says the troops will help law enforcement agencies stem "the flow of trafficked people, criminals, narcotics, weapons, and ammunition trafficked in the state".
McMaster was one of Trump's earliest supporters in the 2016 Republican presidential primary but said there was nothing political about the deployment.
If 4,000 troops were deployed, that would be about double the current U.S. military presence in Syria and about half as many as the number of USA troops in Iraq.
"Your support will free up the border agents to serve on the border allowing us to put more boots on the ground", Ducey said.
His office says guard members will provide air, reconnaissance, operational and logistical support to border patrol agents. He added that there isn't a fixed date for the troops' deployment and they could be stationed for "long haul".
Pima County Sheriff Mark Napier says he sees the border as a security and human rights issue.
Previous border deployments of the National Guard have included barrier installation. Trump called for thousands of National Guard troops along the border last week.
President Trump has said he wants to use the military at the border until progress is made on his proposed border wall, which has mostly stalled in Congress.
Joel Villarreal, the mayor of Rio Grande City in Texas, said he did not agree with what he characterized as "the militarization of the border".