President Donald Trump proposed creating a new branch of the U.S. military specifically for fighting in space. Trump might not have realized it, but he was helping to revive an old controversy.

"Space is a warfighting domain, just like the land, air and sea," Trump told a an audience of military personnel at Marine Corps Air Station Miramar in California on March 13. "We may even have a space force—develop another one, space force. We have the Air Force, we'll have the space force."

But America already has a space force. It's called the Air Force. The flying branch has, over a period of decades, gradually assumed control of most of the military's orbital operations. "The Air Force is the main space force," Brian Laslie, an historian and author of The Air Force Way of War, told The Daily Beast. "And this makes perfect sense."

The Air Force's evolution into a de facto air and space force occurred in parallel with the introduction of intercontinental ballistic missiles and higher- and higher-flying bombers and spy planes. For a period in the 1960s, the Air Force combined ICBMs (which travel through space) and bombers (which can climb to 50,000 feet or higher) in the same units, which it called "aerospace wings."

Today the Air Force develops, launches, operates and protects most of the country's roughly 300 military satellites and other spacecraft. In exchange, it has received most of the roughly $11 billion the Defense Department annually has spent on space programs in recent years.

Moreover, almost all top military officials overseeing space operations are Air Force generals. "For a while, the commander of Air Force Space Command, U.S. Space Command and NORAD were all the same Air Force officer," Laslie explained.

Every so often, lawmakers and military leaders push back against this consolidation, and propose to strip the Air Force of some or all of its space units and reorganize them under a new military branch. The tussle over a space force began as early as 1991, the year the U.S. military leveraged GPS, spy satellites and satellite-based communications to soundly defeat Iraqi troops during Operation Desert Storm.

"Since the end of the war on 28 February 1991, the debate over whether space should become a separate service, equal with the Air Force, Army and Navy, has grown in proportion to its indispensable value to our nation’s defense," Air Force colonel Michael Whittington wrote in a paper in 2000 for the Air War College in Alabama.

The closest reformers came to creating a separate space force was in 2017, when Rep. Mike Rogers and Rep. Jim Cooper—both members of the House Strategic Forces committee—pushed legislation that would create an independent military organization for space operations.

Rogers and Cooper accused the Air Force of leaving America's space assets vulnerable to Russian and Chinese attack. "After months of thorough oversight, it became clear that the Department of Defense, and the Air Force in particular, did not prioritize space capabilities even as threats increase, and were not structured in a way to ensure that we are able to deter, defend and if necessary fight and win in space," the Congressmen wrote in a statement.

“At a time when Russia and China are developing new offensive capabilities designed to deafen and blind America in a future conflict, lack of accountability and leadership on space issues, as well as development and acquisition failures, undermine our national security and leave the country vulnerable," they continued.

With the creation of a separate space force, "the Air Force will no longer be able to treat space as a third-order priority after fighter jets and bombers," Rogers and Cooper concluded.

The Defense Department strongly opposed the space-force idea. “At a time when we are trying to integrate the department’s joint warfighting functions, I do not wish to add a separate service that would likely present a narrower and even parochial approach to space operations," Secretary of Defense James Mattis wrote in a letter to Rep. Mike Turner, an Ohio Republican and another advocate for an independent space force.

But the military had already tacitly acknowledged that Rogers and Cooper, respectively an Alabama Republican and a Tennessee Democrat, had a point. In April 2015, Bob Work, then the deputy defense secretary, cornered Air Force general John Hyten at a symposium in Colorado. At the time, Hyten was in charge of Air Force Space Command.

"You’re not ready,” Work said, according to Hyten. Work told Hyten that his command weren’t ready “to do space operations in a conflict that extends into space.” Not when Russia and China were both developing increasingly powerful satellite-killing rockets and elusive spacecraft capable of sneaking up on, and disabling, U.S. satellites.

Hyten saw Work's point. Beginning in 2015, the Air Force put its thousands of satellite operators on a war footing in order to counter increasingly aggressive Russian and Chinese moves in space. Air Force Space Command organized realistic war games simulating orbital conflict.

At the same time, the branch’s budget requests began to include more funding for satellite defensive equipment, including sensors for detecting an incoming enemy vehicle and thrusters for quickly dodging an attack. The Air Force wants to spend around $8 billion on satellite defenses in 2019, a nine percent increase over 2018.

These reforms weren't enough to deter Rogers and Cooper from pushing their space-force proposal in 2017, but along with Mattis' opposition, they apparently did reassure the U.S. Senate, which ultimately blocked the representatives' proposal ... for now.

But as a consolation to Rogers and Cooper, the Senate added language to the Pentagon's 2018 funding bill that tweaked the Air Force's oversight of military space programs. The 2018 authorization eliminated two senior Air Force space leadership positions and reassigned some of the flying branch's budgeting responsibilities for space programs.

Rogers and Cooper praised the moves as “the first step in fundamentally changing and improving the national security space programs of the Department of Defense and the U.S. Air Force in particular.”

Lawmakers aren't likely to end their push for separate space branch. "This issue is not dead at all," Todd Harrison, an analyst at the Center for Strategic and International Studies, told The Hill.

And now proponents of an independent space force—that is to say, enemies of the Air Force's dominant role in orbit—have a new ally in their fight: Trump.