President Donald Trump announced Monday that he is directing the Pentagon to establish a “Space Force” as the sixth branch of the armed forces — but the move is not as simple as his announcement suggested, and it's far from done yet.

The big picture: It wasn’t clear on the day of the announcement that Trump had signed a directive for the Pentagon to actually create the force — and the Pentagon is treating Trump's announcement as "guidance." Any creation of the force would also require congressional approval, and it's unclear at this time if the support is there to split a fully-fledged "Space Force" off from the U.S. Air Force (USAF), where military space operations are currently housed.

The bottom line: The personnel, budgeting, capability, and operations planning that would have to go into this decision cannot be completed with the stroke of a pen.

A smart take: This is reflective of Trump’s management style, the WSJ’s Andy Pasztor and Gordon Lubold write: "He occasionally offers seemingly ad hoc ideas in public, but at some point expects aides and cabinet officials to follow up with specific implementation plans."

It's not a total surprise from Trump. He has floated the idea before — first in March at a Southern California air base, and then again this May at a White House reception.

The pushback: There are undertones of resistance at the Pentagon among top military brass — generals have told Sen. Bill Nelson they do not support the move.

The Pentagon's official line: "We understand the President's guidance. Our Policy Board will begin working on this issue," said Dana White, chief Pentagon spokesperson.

"We understand the President's guidance. Our Policy Board will begin working on this issue," said Dana White, chief Pentagon spokesperson. Defense Secretary Jim Mattis said in a letter to the Senate Armed Services Committee last year: “I opposed the creation of a new military service…at a time when we are focused on reducing overhead..."

said in a letter to the Senate Armed Services Committee last year: “I opposed the creation of a new military service…at a time when we are focused on reducing overhead..." The Air Force: Just a week before Trump made the announcement, Air Force Secretary Heather Wilson met with the service’s senior commanders, and the conclusion was that “this will happen, but now is not the time,” a person who participated told the WSJ.

The history: It is possible to separate out some capabilities from existing branches of the armed forces and form new ones. The USAF was first created as a separate entity from the U.S. Army in 1947. Over the years it gradually acquired new capabilities, including missile operations, intelligence satellites, and, in 1982, the creation of the Space Command, headquartered at Peterson Air Force Base in Colorado.

Yes, but: The baseline in international law leaves it unclear whether space can be used for military purposes, and there’s no general consensus among experts who analyze this issue, according to the International Committee of the Red Cross.

The 1967 Outer Space Treaty contains no language that specifically prohibits militarizing space, except when it comes to weapons of mass destruction, like nuclear weapons. It is required that all states’ use of the Moon and other celestial bodies is for “peaceful purposes.”

Exploring and using outer space must be done for the benefit of all countries and all exploration and use must follow international law, like the U.N. Charter, per the treaty.

Why it matters: China has vowed to shoot ahead in the race to gain technical acumen in space. On Friday, after Trump announced his guidance, NASA Administrator Jim Bridenstine discussed China’s and Russia’s ability to threaten American space assets Friday before Congress.