There are still questions over whether the North can shrink a nuclear weapon to fit atop its intercontinental missiles, or keep it from burning up on re-entry into the atmosphere.
But at the Pentagon and inside American intelligence agencies, there was a sense that the North had now crossed a threshold it has long sought: Demonstrating that if the United States ever threatened the regime of Kim Jong-un, the North Korean leader, it had the ability to threaten death and destruction in the continental United States.
The United States has lived with that threat from Russia and China for decades, but the last four American presidents have all said the country could not take that risk with a government as unpredictable as North Koreaâs.
Hours after Fridayâs test, former American officials said President Trumpâs options were limited.
âIn the White House you have a threshold decision: Can you get them back to the table or not,â Mark W. Lippert, President Barack Obamaâs ambassador to Seoul, said Saturday about negotiating with the North Koreans â a step Mr. Trump said during the 2016 campaign, and again several months ago, he was willing to try. Mr. Lippert said he supports Washingtonâs current diplomatic efforts as well as United Nations sanctions against the North.
But so far, the North has not responded, perhaps calculating that it first wanted to demonstrate it was a permanent member of the club of nuclear-armed nations, and able to strike American cities, to strengthen its position before any negotiation.
Mr. Lippert, speaking at a conference in Kent, Conn., said that barring negotiations, âthe question gets binary pretty quick: containment…