High Probability of New Terrorist Attack?

I'm not quite sure what Nate Silver is talking about here:  

natesilver: I mean, the probability of an actual or thwarted terrorist attack in the U.S. or in some  NATO country over the next year or so has to be quite high. I’m not talking about something on a 9/11 or a Paris scale or anything like that, but something scary enough for Trump to use it as a cudgel to try to expand his powers. [emphasis added]
https://fivethirtyeight.com/features/what-really-matters-from-trumps-first-3-weeks/

The Paris attacks involved 3 attackers, the 9/11 19.   The Orlando attack involved one, but killed 49.

Certainly there's some terrorist attack which could prompt Trump to ask for/get expanded powers, but what would it be?

Some possibilities:

• a multi-person attack by refugees admitted before 2017 from one or more of the seven countries
• an attack which claims victims in the triple digits or more, particularly if multi-person.
• an attack on a particular target, like a sporting event, a civic event, a notable politician or eminent figure.

Hindsight is 20-20, but I'm pretty sure in the months after 9/11 I was more optimistic than most about new terrorist attacks.  But I'm still surprised we've gone 16 years with only lone wolf (regarding San Bernadino as one) attacks, attacks with little innovation as to targets or methods. So my predictions for the future have very low confidence, but I'd still expect more of the last 15 years than anything which could be a pretext for more surveillance, enhanced interrogation, etc.