Actually that is The Easiest Way to get a Nuke or dirty bomb in to The US.
It is arguably one of the more poorly defended borders in the world. One need only realize the tons of Heroin and semi trucks full of illegals that flow across the border daily to understand that.]
Without going into details(because why give terrorists ideas), I have thought easily of 4 much easier ways to get a nuke into the United States.
And 'more poorly defended borders in the world'? Our border with Canada is far less defended.
'semi-trucks full of illegals'?
You mean the ones caught by CBP at the border? Semi Trucks coming across the Southern border all go through radiation detectors, and a huge percentage under go x-ray type inspection.
Between obsessing over the southern border(the least likely route for a nuke), or obsessing over refugees(the least likely way a terrorist would enter the U.S.), its like Conservatives want the U.S. to focus on everything but the least likely possibility of attacks on America.