They have the ability to deliver a nuclear weapon into the United States...

No matter how many billions of dollars are spent, it is almost impossible to prevent delivery and assembly of the material need to build a nuclear bomb to the United States.

There are two main reasons for this.

1.  Needle in a haystack.  A single suitcase can easily hold enough nuclear material to make a bomb.  And over 50,000 large containers (20 or 40 foot metal boxcars), containing over 500,000 boxes enter the borders of the United States every day.¹  No matter how much is spent on security, only a small fraction of those boxes can be inspected, and only a tiny fraction of those can be inspected carefully.

And even if a box with the radioactive nuclear materials was inspected...

2.  It is difficult to detect radioactive material if it is properly shielded, such as putting it inside a lead box.  The walls of the box absorb the radioactive particles so that they do not escape.   No alarm will go off.²

In fact, this has already been accomplished - easily.  Close to one year after 9/11, ABC News shipped 15 pounds of depleted uranium (with the same radioactive signature of bomb-making uranium) from Turkey to New York.  Although the cargo container with the uranium was inspected, the uranium was not detected by the inspectors and was allowed to pass into the country.³  ABC News repeated the test a year later on August 23, 2003, shipping it in a furniture trunk from Jakarta, Indonesia (high on the U.S.  list of terrorist centers).⁴ Once again, the uranium was not detected and crossed the border into the country.

In spite of our best efforts and spending several billion dollars a year, hundreds of thousands of illegal immigrants cross the border into the U.S.  every year.  Over 21,000 pounds of illegal drugs cross our border every day.⁵   Preventing a small group of well-financed terrorists from entering the country is tough.  Preventing them from smuggling in a single container of shielded nuclear material - nearly impossible.

Furthermore, once a nuclear bomb is put together and placed in a city, even if it is not shielded, it is still very hard to detect because of all the other small sources of background radioactivity, such as freshly paved roads, polished granite, dinner ware and, medicines.  Unless the government knows to within roughly ¼ mile where the bomb is located beforehand, we cannot determine where it is even if we know in advance it is going to be detonated.  ⁶