Read Defense Secretary James Mattis' statement warning of the 'end of the North Korean regime' |...

This is mutually assured destruction without the mutual. The DPRK views Guam as a military installation (which much of it is) and not a piece of sovereign US territory. Note the absence of threats against Okinawa, where we have a boatload of Marines and other assets based. Okinawa is sovereign Japanese territory, which the DPRK does not wish to mess with (for now).
This is a grave mistake on their part, as Guam has over 160k US citizens in residence. Hitting it would be no different than hitting Hawaii or Alaska and would be tantamount to a declaration of war. We would have no choice but to seriously rearrange their landscape if such an attack were mounted.

LTC Ivan Raiklin, Esq. Most people took POTUS' words as 'bluster'. However, it took a vastly more serious turn now that SecDef is confirming said words. We've pussy-footed w/ sanctions & "red lines" since the 90s when Clinton gave NK 2 nuclear reactors. Anyone w/ any damn sense could tell what they were going to do w/ those reactors, but our leaders just shook their finger and reset the red line.
Let's not forget, the Korean Conflict never truly ended, we've just been under an extended cease fire.