Sounds like this guy was radicalized over a period of years, not overnight. I saw one news story (I can't find it now) that quoted family as saying he had been obsessed with ISIS for the past year. And according to ABC,No need to go off track with much of a discussion about that here, but Dylan Roof was clearly a troubled dude. He also apparently, for a considerable period of time, consistently held white supremacist beliefs and committed the shooting motivated by those beliefs.
Now I don’t know enough to come to any conclusion about this guy yet, but he voiced frustration about his divorce and discussed wanting to kill his family in a “celebration.” Then he discussed having a dream about joining ISIS, like he just had that dream and planned to join ISIS on a whim. And his plans suddenly changed from killing his family in that “celebration” to carrying out the act he committed. Those reports suggest erratic behavior that does not involve much “political” or cohesive thought.
"A senior official told ABC News that authorities currently believe Jabbar was radicalized in the last few years — and that radicalization may have been exacerbated by the Israel-Hamas war."
What we know about Shamsud-Din Jabbar, the suspect in the New Orleans attack
The suspect in a deadly attack in New Orleans has been identified as Shamsud-Din Jabbar, a 42-year-old U.S.-born citizen from Texas, according to the FBI.
abcnews.go.com