It would invoke broad presidential powers to bar foreigners from entering the country for national security reasons - under the same section of immigration law that underpinned the travel ban - to block Central American migrants from crossing the southern border, they said.
The sprawling caravan of migrants -once estimated by the United Nations to be more than 7,000 strong - is hoping to make it to the United State.
Trump previously said he would send the military to the border if Mexican authorities failed to stop the caravan, which they have.
Candy Guillermo, a 37-year-old migrant in the caravan who had heard about the plan to deploy troops, was surprised she and the children in the group would be considered a threat.
Trump tweeted Monday that he'd alerted the military that the situation was a "National Emergy" - but the Pentagon said then that they'd received no new orders to provide troops for border security.
"Trump should be more humanitarian", she said.
In a tweet sent on Thursday, President Trump addressed the migrant caravan directly, advising them to follow the laws of the United States and apply to come in legally. "We only want to give our kids a better future".
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A recent study found that counties that went for Trump saw higher rates of bullying as kids feel empowered to act "presidential". Alexander recalled in a written statement only that the woman in front of him had spoken to him and then changed seats.
One piece of the action under consideration would use an authority similar to that invoked by the travel ban, which would block entry to unauthorized immigrants who are not yet in the USA, said the three sources.
Under standard USA procedures, the migrants, assuming they reached the southern border, would be detained for not having the required documents and asked whether they are afraid of returning to their home.
The executive action would reportedly involve Homeland Security and the Justice Department issuing a rule, effective immediately, that limits foreign nationals' rights to seek asylum in the US if they are a part of a population banned by Trump, sources familiar with the administration's plans told the Chronicle.
But Nielsen warned: "This caravan can not come to the United States". That's almost double the asylum claims the USA fielded in 2015 and almost quadruple the claims in 2013.
The ones from Texas aren't armed and are helping in key support roles such as running motor pools so more Customs and Border Protection agents can work directly along the border, said Texas Army National Guardsmen spokesman Maj.
In April, Mattis authorized as many as 4,000 troops to the border, pending approval of certain state governors, many of whom approved. So far, only a little over 2,000 have been used.
Trump told a rally crowd in Wisconsin on Wednesday that the military was "all set". "You're going to see a very secure border", he said.