The Pentagon couldn't say Thursday when or where National Guard troops would be deployed to the Mexican border, how many of them would be called up, how long they'd be there, how much it would cost, whether they'd be armed, or what exactly their mission would be.
"We want to do this immediately," said Dana White, the Pentagon's chief spokesperson, but "those are the questions we're working to resolve right now. I don't have the answers for any of those."
President Donald Trump later told reporters aboard Air Force One that about 2,000-4,000 troops would deploy.
"We're moving that along," he said.
Trump gave no estimate for the duration of the deployment but said some of the troops would probably stay "until such time as we get the wall" that he promised to build along the border during the campaign.
A day after Trump said troops would go to the border ahead of his proposed border wall, White said the details of the deployment would be worked out by the Pentagon's new Border Security Support Cell.
The 24-hour cell, headed by Assistant Secretary of Defense for Homeland Defense and Global Security Ken Rapuano, will serve as the "single conduit for information and coordination" between the Pentagon and the Department of Homeland Security, White said at a Pentagon briefing.
"The president has authorized the National Guard, with the affected governors' approval, to enhance its support to CBP (U.S. Customs and Border Protection) along the border," White said. "The National Guard's efforts will include aviation, engineering, surveillance, communications, vehicle maintenance and logistical support."
"These National Guard members will act in support of Border Patrol agents who are performing law enforcement duties," she added. "We will focus on supporting CBP's priorities, which will determine the time frame and number of military personnel employed."
Marine Lt. Gen. Kenneth McKenzie, the director of the Pentagon's Joint Staff who joined White at the news conference, said it had not yet been determined whether the troops deployed to the border would be armed.
In a statement, Mexico's Foreign Ministry said Wednesday night that it had received assurances from the Trump administration that the Guard troops would not be carrying weapons.
At a White House briefing Wednesday, Homeland Security Secretary Kirstjen Nielsen said that National Guard troops could start deploying to the border as early as Wednesday night, but White said Rapuano and Homeland had yet to coordinate with the border state governors who would approve the callups of the Guard.
In addition, there was the possibility that Gov. Jerry Brown, D-California, might delay his approval or refuse to cooperate.
Trump also appeared to back off on the urgency of the National Guard deployment in lieu of the "big beautiful wall" he pledged to build during the campaign and have Mexico pay for it.
In an early morning tweet, Trump said that the "Caravan" of immigrants from Central Americans, mostly Hondurans, that had been moving north through Mexico had mostly dispersed, and he lamented that Mexico appeared to have stronger immigration laws than the U.S.
"The Caravan is largely broken up thanks to the strong immigration laws of Mexico and their willingness to use them so as not to cause a giant scene at our Border," he said. "Because of the Trump Administration's actions, Border crossings are at a still UNACCEPTABLE 46 year low. Stop drugs!"
At a forum in White Sulphur Springs, West Virginia, later Thursday, Trump said that eventually "We're gonna have the wall."
"The military is going to be building some of it," he said. I think over the next 12 months we'll have a lot of things happening."
However, it was unclear whether the military had the authority to build on land near the border.
At the White House briefing Wednesday, Nielsen said parts of the wall might go up on land controlled by the military along the border
White said Thursday that the Pentagon was looking at the vast Barry M. Goldwater training range in the Sonoran desert south of Luke Air Force Base in Arizona, but she was not sure whether the military actually owned the part of the training range abutting the border.
The U.S. has periodically sent troops to the border to assist the Border Patrol with surveillance, intelligence and logistical support. Both the White House and the Pentagon noted that Guard troops were deployed in the administrations of former Presidents Barack Obama and George W. Bush.
In 2010, Obama sent 1,200 to the border and Bush sent about 6,000 in 2006. According to a Government Accountability Report, the Obama deployment helped the Border Patrol apprehend
25,514 illegal immigrants at a cost of $160 million.
In the Bush administration's Operation Jump Start, about 6,000 troops were sent to the border between 2006 and 2008, at a cost of $1.2 billion.
Under rules of engagement set by the Pentagon for the Obama and Bush deployments, Guard troops were not allowed to pursue, confront or detain suspected illegal immigrants, investigate crimes, make arrests, stop and search vehicles, or seize drugs.
In addition, they could not check Mexico-bound vehicles for bulk cash or smuggled weapons headed to the drug cartels.
At the Pentagon Thursday, White and McKenzie said the rules of engagement for the current deployment had yet to be worked out.
"We'll work in conjunction with the governors who are in fact on the front lines to see what they need, and work it within the National Guard," White said.
-- Richard Sisk can be reached at Richard.Sisk@Military.com.