I don't know. They did it with all other immigrants before them. People from known communist countries went through much greater scrutiny than muslims go through today. We certainly did. There is a point where you should perhaps pay attention.
Hell, when my dad applied at NASA, they turned him down, because he was from a commie country. Ironic since this man designed missiles, planes and spacecraft in his youth... with pencil and paper, not CAD software. Stuff that WORKED, mind you. This being ironic that NASA was founded by NAZIS (look it up, I found it out later) and staffed by people who were opposed to russian influence, not actual socialism (which they embraced whole heartedly.)
Ironically, some of the citizenship and immigration questions are idiotic. "are you against the violent overthrow of a legitimate government?" Seriously? Since when has the USA not been doing EXACTLY THAT? (Coincidentally, if you answer yes, you are singled out for "further screening." Guess they want to find out if you want to join PNAC and become a policy maker for the USA, eh?

) Other questions: "are you a terrorist or have you ever received training at a terrorist camp?" Yeah. Let me

again.
The only thing that could help here, is if people want to come forward and rat out their terrorist buddies, or people lie and then it gets found out later. Most of it is security theater. Kabuki as ML calls it.
Just like the commie scare in the 50's through the 90's... the commies came here in Abraham Lenin's time, and America became a statist place since, with only the vast wealth left to steal that kept it from immediately becoming the slowly decaying pit of ever more numerous tax fed parasites, which it has since become.
Thomas Paine was right. We had it within our power as a society, here in the west, to reboot civilization and start it clean and right. Without religious fanaticism, without stupidities, without the morally failed theologies and ideologies of the past.
I'm here to say they failed miserably.