The reason this is such a big deal is because there are parts of a nuclear bomb that have a shelf life; most importantly, the neutron moderator like beryllium tampers, that slow down the neutrons to allow for the uranium to achieve critical mass and go boom. The U-238 also degrades over the years. Finally, new designs make weapons more efficient - more bang for the buck.

While the new START treaty will forbid the construction of new weapons, there may be a work around.

Nuclear weapons are complicated; the older they get, the less sure you can be that they still work. One way to know is to test them, but there is no appetite in this country to resume testing (which we unilaterally halted in 1992).

Another option is to do what we are doing now: conduct an extensive maintenance program to identify problems and replace degraded components. But that doesn't yield certain knowledge; it only raises confidence. Yet another way would be to make more warheads. That's what Secretary of Defense Robert Gates wanted to do when he was serving in the prior administration and reportedly still supports.

It's also what every Republican senator plus Joe Lieberman says will be the price of ratification of the New START treaty. But the Nuclear Posture Review emphatically says "the United States will not develop new nuclear warheads." Game over, right?

Well, it depends on the meaning of "new." The approach favored by Gates-called the Reliable Replacement Warhead (RRW)-would use existing fissile material, parts stripped from decommissioned weapons, and design specifications that were developed decades ago. If a skilled mechanic were to build a car using spare parts, old steel, and blueprints from a 40-year-old file cabinet, would it be a new car? In one sense, yes. In another sense, no.