So...they're redoing the NASA split?
Sounds like this is different, although poorly thought out. NASA was created when it was clear there was a legitimate civilian interest in space exploration. That's not to say it was an entirely cut and dry split either, they still work closely together. The Shuttle program was notable in that to get it funded it was also partially a military project and thus had to meet certain requirements set forth by the Air Force. (Requirements, which honestly hindered it in some ways for its civilian purposes, but that's another story.)
I won't say it can't be done well, but as it stands the Air Force does a more than sufficient job of dealing with space. There's also the fact that a lot of what they do would likely still be connected closely to a separate space branch. It would have to be to avoid serious costs with doubling up on efforts. The other alternative is to gut the Air Force so completely that they would no longer do ANYTHING other than fly planes. That would mean breaking off the ballistic missiles and missile defense. Communications and Spy satellites. Certainly other things as well. Given that most other branches already fly their own aircraft it almost leads to the question of what is the Air Force even there for if you take space from them?
It also completely throws out the window the current facade of space as peaceful place of international cooperation. While it's obvious all spacefaring nations have been more than happy to use space for military purposes, at the very least with communications and surveillance if not more, and in at least a few cases demonstrating force in space with destruction of satellites. It seems like it would be yet one more step, and a bad precedent to set up an entire military branch dedicated to militarizing space.
Now here's my 100% conspiracy theory nutjob idea:
NASA was ordered to stop studying the earth itself and focus outward. Trump wanted to heavily cut funding from other government science agencies especially those studying the environment. That leaves the military as the last uncontrolled government group really focusing their eyes on the earth. The navy and the air force in particular do spend significant money on atmospheric and oceanic observations, often with satellites. Any congress, but a republican controlled one especially is going to have a hard time cutting funding for the military... but if they were to instead... perhaps... break off some stuff they wanted to control into a new branch, with a new rule book written to their tastes. Military spending would go up as a whole, while at the same time funding for certain projects, namely environmental science related ones, can go down.
EDIT: Awkward wording.