North Korea has successfully tested two intercontinental ballistic missiles and a nuclear bomb with way more destructive power than those dropped on Hiroshima and Nagasaki. North Korea nuclear threats to U.S.A are very serious.
U.S.A Defence Strategy Against North Korea Nuclear Attack (Infographic)
And the United States is worried about those threats, it’s not that U.S haven’t been working to defend itself other than politics. United States has already implemented ways to defend itself against North Korea nuclear threats with some strategies.
See the infographic below to understand how would U.S. be defending itself if North Korea attacks a nuclear missile on United States of America.