Earlier quoted context omitted.
Ordered by likelihood would be 6, 2, 1, 5, 4, 3 - 6.) being unfortunately a given (the question being where and when they'll attack) and and 3.) not very likely.
Why do you think 6 is a given? Has political tension in the US just got to breaking point?
The issue is that the right wing has steered very hard into anti-gay rhetoric in the last couple of cycles which convinces the sort of deranged people who commit mass hate attacks that they are doing something for a cause.
Combine that with the fetishization and availability of military style weapons and it’s pretty easy for a lone miscreant to kill a lot of people fast.