Trump is known for his bombastic warring rhetoric. But when he is cornered with no military options he talks like this. Endlessly. A crybaby. 

The only military option is for the U.S. to attack NK alone. Because SK and Japan will not join, and SK will not initiate war. If U.S. does attack it will 1) cause a devastation and bloodshed greater than Vietnam War for NK, SK, Japan and the U.S. itself'; 2) will lose military alliance with SK and Japan; 3) will trigger a military response from China and Russia (this is confirmed officially by them). It will trigger WW3. And thus all U.S. assets around the world will be subject to  attack. 

Faced with this, Trump talks, yell and threaten. This is all he can do. Besides, U.S. Navy in Asia Pacific is currently in one holy mess.