NK has been making threats and posturing for decades. US policy up until now has been “Don’t feed the trolls.”
But like your drunk cousin on facebook, he decided to reply with the, “Fuck all y’all!”
Here is the deal, the US can not and will not do anything directly. If NK gets to the point they are fucking up things out side of their sand box, China will HAVE to step in as they have sooo much power over them (90% of their trade and helping to prop them up in the past.). That and they don’t want a US presence near mainland China.