The last 2 big attacks were done by US citizens in Orlando and San Bernardino were citizens, they became radicalized and in one case the wife made a pilgrimage to Pakistan. This is when you have to be careful, citizens with family ties to region going back to regions. People are trying to come over due to being killed and their kids being slaughtered. They just want safe havens to live.
There is enough blame to go around, we have turned our back for years on Iraqi's people, the Kurds have been slaughtered after years doing our dirty work for us. We have totally for the last 5 years mangled all good ties by turning our back on Syria and other safe zones. Just left them out to dry. Yeah Isis hates us pretty bad but now you have people who were our allies who are being hurt and US has totally turned back and left it to Russians, Syria to kill and take over. These people who were giving us help now don't trust us and hate us do to last actions, their kids grow up to hate us and blow up buildings. Trump pretty much called the FBI and CIA awful during campaign.
I am not some bleeding left wing, Your experts and most of the retired generals are all of opinion you don't have enough bullets to kill every one, you do it by giving these people safe places to live, water, food. You don't go against a whole race like Trump did. Shameful.