Note that firing a few missiles into the sea, and some (semi-)successful tests does not indicate the capacity to actually hit targets, like say, the continent of North America.

The USSR was never very good at hitting its targets with ICBMs, so they would barrage targets with multiple redundant warheads. They needed twenty missiles to hit a target to our one, a situation that General Electric manipulated to fuel the escalation war between US and USSR in the 1980s. (Reagan was into it, and believed he was going to play a part in God's Armageddon by launching a retaliatory strike.)

US Polaris missiles are accurate enough to hit a phone booth. It'd be expensive but we could deliver Kim Jong-Un a pizza by Polaris if we really wanted to send a message. (We'd have to find a save place for the ICBM fuselage to drop, and we'd scare the snot out of NATO.)

Because we've been kicking the can into the future for so long, regarding dealing with the North Korea problem (which means also an ugly meeting with China), it may be useful to US politicians to allow the fiction that DPRK could attack us if they wanted to, despite how it would not go well for them, even if we responded only with conventional weapons, because yes, it allows Trump (or whoever is in office) to save the US from alleged calamity.

That all said, Trump really liked correspondence with Kim Jong-Un and so by a few letters of flattery Kim was able to secure foreign aid from the US for a while without having to resort to threats of causing disaster. Still, I remember Trump's fire and fury speech, which made it looking like the US had elected a pro-wrestler to president... I guess we actually did that.