The main obstacle for ISIS doing shooting attacks in the US is that they may just blend in with all the other mass shootings in the US.
Imagine the interrogation:
"Why did you shoot all these people?"
"American women are sluts!"
"You're not really distinguishing yourself with that crazy complaint."
"So seriously, give us a unique reason: why shoot all these people?"
"Your government is CORRUPT!"
"Uh...concentrate and try again?"
"Okay, one last time, one good reason why haven't heard before: Why shoot all these people?"
"God demands it."
"Now you're trolling us."
Imagine the interrogation:
"Why did you shoot all these people?"
"American women are sluts!"
"You're not really distinguishing yourself with that crazy complaint."
"So seriously, give us a unique reason: why shoot all these people?"
"Your government is CORRUPT!"
"Uh...concentrate and try again?"
"Okay, one last time, one good reason why haven't heard before: Why shoot all these people?"
"God demands it."
"Now you're trolling us."