We’ll just put this one in the “we’ll see” file of endless absurd claims Trump makes and you believe (like a sucker) that never materialize.
You are looking for a binary answer to match your binary mind.
In the real world, there are complexities. Trump has powers at the border but cannot supplant civilian powers. This was fully discussed yesterday. In addition, although the posse comitas act prohibits certain federal actions.....use of the national guard etc.....it allows for the use of national guard under federal command where THE GOVERNORS OF THE STATE REQUEST OR APPROVE. So obviously that poses different possibilities in Texas and Arizona than for California, as examples. Wayyyy too many factors at play for your binary mind.
In addition, although Trump probably cannot supplant border patrol and civilian arrest and detainment functions, he most likely can use military personnel and resources and intelligence gathering capabilities in support functions. So, again, a complexity that cannot be processed by a binary mind.
In general, you have to see what is support versus direct engagement with illegals and you also have to see what is considered to be short term versus long term. Both Obama and Bush used the military to train border patrol at certain times and the Army Corps of Engineers has been involved in wall design and maintenance at times. Although these functions are outside the core mission of the military they have been allowed/tolerated if it is a transitional or temporary plan. Trump, for example, would probably be on shaky grounds if he announced that the military was going to take over responsibility for the southern border but if he identifies problem spots and says the military will be assigned there while the wall is being built there, then that is another matter.
In addition, the posse comitas act is just legislation. Not constitutional scripture. It can be altered or re-affirmed as needed as part of changing current immigration law to get rid of the some of the foolishness.
I know this is way too complex for the binary mind and you are looking for a bumper sticker answer as to what lies ahead or a bumper sticker answer as to what the feds and the president cannot do. Sorry. This world was not designed for you.
In addition, the posse comitas act would be unconstitutional where it prohibits a president from performing a constitutional mandate to protect the country from foreign forces. As discussed yesterday, mexico needs a good nafta deal so they will disband the caravan clown show, but as a possible/hypothetical if the number headed here was 10,000 rather than 1,000- then not only could the president use troops but he could also send troops into Mexico to disband or contain or capture them there.