To me, what I find extremely distasteful was his use of the phrase "as the world has never seen"--twice! When I heard him use that phrase my mind immediately jumped to the events at Hiroshima and Nagasaki. You can bet that was his intention in his little mind.

For the President of the US to evoke those events in a public threat was un-presidential, and in horrible taste. He's basically saying "remember what we did to Japan? That was nothing!"