The reason that Islamist militants can assert that jihad is necessary against the perceived enemies of Islam is that there is sufficient ammunition in the Quran to buttress their beliefs. The same could also, of course, be said for the Old Testament, which is full of scenes of violent death visited on the enemies of God.
The diagnosis that poverty, lack of education, or lack of opportunities have much to do with terrorism requires a fundamentally optimistic view of human nature. This diagnosis leads to the prognosis that all we need to do to solve the terrorism problem is to create societies that are less poor, better educated and have more opportunities.
Trump, of course, has been very wrong in the past about important issues such as President Barack Obama's place of birth and Mexican immigrants, but the Republican frontrunner is correct in saying that former Republican President George W. Bush did not keep the country safe during the 9/11 terrorist attacks.
What made al-Awlaki so influential is that, unlike a number of leaders of al Qaeda such as Osama bin Laden, he was a cleric, so he could present himself as a leading religious figure. Second, because al-Awlaki had spent much of his adult life in the States, he communicated with his followers in colloquial, accessible American English.
The dangers of TATP bombs can be seen in the case of Matthew Rugo and Curtis Jetton, 21-year-old roommates in Texas City, Texas. They didn't have any bomb-making training and were manufacturing explosives in 2006 from concentrated bleach when their concoction blew up, killing Rugo and injuring Jetton.
President-elect Donald Trump has a host of national security challenges to deal with as he assumes office, from the resurgence of the Taliban in Afghanistan to the grinding Syrian civil war to the flexing of Russian muscles under President Vladimir Putin to how to deal with ISIS as the terrorist army retreats in Iraq.