This missile could reach US but can N Korea use it with a nuclear weapon?

North Korea is speeding toward a goal it has sought for decades: the ability to hit a major American city with a nuclear weapon.

Actually striking the United States would be suicide. But the capability could help the North deter an invasion and wield increased global influence. American intelligence agencies estimate that the North could reach the milestone by next year, and some experts think it already has.

But reliably sending a nuclear warhead halfway around the globe is extremely difficult, and challenges may remain. Here are some of the systems the North needs to advance or master.

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