2007 Chinese anti-satellite missile test
While it was overwhelmingly condemned by the international community, it still happened. Not really sure exactly what a "Space Force®" would do to prevent this sort of thing from happening, but a dedicated group working to identify a vulnerabilities and exploring defenses might be appropriate. Trump's ham-handed delivery not withstanding. Remember, he a marking guy. And marketing guys think everyone is as dumb as they are, so everything has to be a slogan or catch phrase (or hashtag).
Again don't get caught up in this idea that somehow this was something Trump thought up all by himself. I'm sure he's had meeting with defense department officials and Boeing lobbyists who made sure this was front and center on his agenda.
From Wikipedia: In January 2001, a (US) congressionally mandated space commission headed by Donald Rumsfeld recommended that “the U.S. government should vigorously pursue the capabilities called for in the National Space Policy to ensure that the president will have the option to deploy weapons in space to deter threats to, and, if necessary, defend against attacks on U.S. interests."