When Donald Trump in December called for "a total and complete shutdown of Muslims entering the United States," I replied that changing just one word – "Islamists" instead of "Muslims" – would transform his outrageous and dead-end effusion into a politically feasible and operationally viable policy idea.

Trump's statement, posted on his website.

In response, came this valid question from readers: And how does one distinguish between Muslims who are Islamist from those who are not? This is a very doable task, though an expensive, time-consuming one demanding great skill.

By Islamists (as opposed to moderates), I mean those approximately 10-15 percent of Muslims who seek to apply Islamic law (the Shari'a) in its entirety. Islamists, not all Muslims, are the modern barbarians; they, not all Muslims, must urgently be excluded from the United States and other Western countries.

Both in-depth research and intensive interviews are needed before allowing aliens into the United States. The process should start with an inquiry into the prospective immigrant's family, friends, associations, employment, memberships, and activities. The immigration services should look for anomalies, gaps, questionable activities, and dubious relationships; when it finds these, it must probe them.

It's no longer just public figures such as intellectuals, activists, and imams whose thinking can be traced, but most everyone, thanks to the proliferation of social media (Facebook, Twitter, etc.), plus the Internet's open invitation to everyone to comment in writing or on video in a permanent, public manner.

In the case of virulent, overt, outspoken jihadis, this research usually suffices to provide the evidence to keep them out. Even some non-violent Islamists proudly announce their immoderation. But most Islamists adopt a milder and subtler tone. Research often proves inadequate in these instances because cautious Islamists hide their goals and glibly dissimulate. Assuming that lawful Islamists routinely hide their true views, a (voluntary) interview is needed and it must be very rigorous. ...