No, because I don't think they'll use a missile.
Our borders are open; the low-tech, low risk option is to just sneak one into the country and have an Islamic martyr detonate it at an appropriate time.
Think Times Square on New Year's; the Superbowl; the next Presidential Inaugeration; the next State of the Union speech.
Lots of options to kill lots of people, all with a basically untraceable nuke.
The enriched uranium won't be traceable because it'll be from a source that's never been sampled. Think NK or Pakistan or even Iran.
They might even be able to buy a small weapon from some former world power's old inventory. Then the signature off the uranium will point in the wrong direction.
As I said, I think it'll be very, very hard to be 100% sure who did it.
So what then? Nuke 'em all? Who's "all"?