President Trump talks about extreme vetting, and we actually do have extreme vetting when it comes to refugee resettlement. Refugee resettlement is the most thorough, cumbersome, multilayered vetting system we have for the admission of anyone to the country.

We are very definitely in a new phase in the global terrorist threat where the so-called lone wolf could strike at any moment.

I think that the potential for homegrown terrorist attacks is something that we have to be very concerned about, because, in many respects, it's harder to detect when you have an independent actor who may be living in our midst, in our own communities.

In my view, and in the view of a lot of intelligence experts, the terrorist threat that we face now has morphed significantly from the days of 9/11 to homegrown violent extremism. We have to be concerned and focused on homegrown violent extremism, countering violent extremism that exists within our borders.

The good news is that the international coalition, in which our military contributes, has done a lot to reduce the ground space, the territory in Iraq, Syria that ISIL once occupied a couple years ago. That's a good thing. And a lot of that, frankly, has occurred in Trump administration, so I'll give them credit for that.

I'll never forget what a Catholic priest told me; he said, "If you try to padlock the door, you have to give people an alternative path - an alternative, safer path. You can't padlock, and you shouldn't padlock a burning building."

With every case from years ago there should be lessons learned.