There's no Uke Nuke on US soil brotha..... for a number of reasons.
At or near the top of that list- nobody is bringing in a bomb and then playing "hide the Easter egg" with it. That's movie sh!t.
If a nuke made it into our borders it would immediately be transported to the nearest mega-city- and set off within an hour of its arrival. Maybe sooner, if the designated bomber was on a suicide mission. You don't leave those just lying around, waiting for DOD or the Feds to figure out where you hid it. Losing a stolen nuke to the Americans because you were too stupid to set the damn thing off would be the biggest counter-intellegence victory in the history of our country. All terrorist groups would suffer from an utter failure of that magnitude. You'd be seen as the dumbest terror group in history.
Think about it- you finally get the holy grail of terror weapons and you can't set it off because you hid it in a parking garage in DC and someone caught you and disarmed it?
Or you get pulled over in Lincoln, Nebraska while you're making an 1800 mile drive from the Mexican border to Chicago...... with a nuke in the trunk.....
Nah.
Nuke makes it over the border then either San Diego, LA, Phoenix, San Antonio or Houston are done. If I'm a terrorist, I'm headed straight to Houston. Drop that sucker off just east of downtown. Cripple all the oil refineries along the coast. Destroy the HQs of several big oil companies. Wreck the 4th largest shipping channel in the US. And take about 2 million civilians with you.