Army head football coach Jeff Monken listens as President Trump speaks during a ceremony to present the Commander-in-Chief’s Trophy to the U.S. Military Academy’s Black Knights football team Tuesday at the White House. (Evan Vucci/AP)

President Trump mused again Tuesday about adding a new branch of the military — a Space Force — and this time made clear he is thinking seriously about it.

Trump aired his thoughts during a ceremony at the White House, where he presented the Commander-in-Chief’s Trophy to the U.S. Military Academy’s Black Knights football team for its victories over Navy and Air Force.

Surrounded by West Point cadets in the Rose Garden, Trump talked up the mission they have ahead.

“You will be part of the five proud branches of the United States Armed Forces: Army, Navy, Marines, Air Force and the Coast Guard,” Trump said.

After a short pause he continued: “And we’re actually thinking of a sixth, and that would be the Space Force. Does that make sense? . . . Because we’re getting very big in space, both militarily and for other reasons. And we are seriously thinking of the Space Force.”

Trump previously raised the idea during a speech in March at Air Station Miramar in San Diego.

“My new national strategy for space recognizes that space is a war-fighting domain, just like the land, air and sea,” Trump told the crowd of Marines there. “We have the Air Force. We’ll have the Space Force.”

Initially, Trump explained, he had proposed the idea as a joke: “Then I said, ‘What a great idea. Maybe we’ll have to do that.’ ”

Some lawmakers on the House Armed Services strategic-forces subcommittee have been pushing to add a unit to the Air Force that would be dedicated to space, but they have stopped short of endorsing a new branch as proposed by Trump.

The Outer Space Treaty, which the United States signed in 1967, bars states from testing weapons and establishing military bases on the moon and other celestial bodies. It also prohibits the placement of weapons of mass destruction in orbit around Earth.

However, critics have pointed out that, since the treaty has no enforcement mechanism, nothing is really stopping a president or anyone else from militarizing space.

Sarah Kaplan contributed to this report.