By all accounts this guy, upon arriving in the USA in 2010, was not radical or even overly religious upon arrival. He became disillusioned with the West after finding out how hard it was to make it with random labour/driving jobs. He turned to the internet and became radical.
Screening prior to entering the USA would have done nothing here. And yes, Trump is already making a big push to end the green card lottery:
http://www.bbc.com/news/world-us-canada-41825340