He is being charged with attempted murder because he took sufficient actions towards accomplishing his goal. He found out where Justice Kavanaugh lived, procured a weapon, flew across the country, and was within a block or two of the Justice's home when he called 911.
The would be shooter did call 911 on himself so I'd say that this actually does look like the actions of someone who is borderline mentally ill and just ended up drinking too much of big media's hate-laced coolaid.