DEFENSE: Can U.S. defend against North Korea missiles? Not everyone agrees.

Briefing reporters on Wednesday, Pentagon spokesman Navy Captain Jeff Davis said: “We do have confidence in our ability to defend against the limited threat, the nascent threat that is there.”

Davis cited a successful test in May in which a U.S.-based missile interceptor knocked down a simulated incoming North Korean ICBM. But he acknowledged the test program’s track program was not perfect.

“It’s something we have mixed results on. But we also have an ability to shoot more than one interceptor,” Davis said.

An internal memo seen by Reuters also showed that the Pentagon upgraded its assessment of U.S. defenses after the May test.

Despite hundreds of billions of dollars spent on a multi-layered missile defense system, the United States may not be able to seal itself off entirely from a North Korean intercontinental ballistic missile attack.

Experts caution that U.S. missile defenses are now geared to shooting down one, or perhaps a small number of basic, incoming missiles. Were North Korea’s technology and production to keep advancing, U.S. defenses could be overwhelmed unless they keep pace with the threat.

I know people who work on this program, and they’re confident in what they do. That said, there’s probably no bigger pucker factor than spending a couple of decades working to stop a hypothetical nuclear threat — and then watching it become real.