Meanwhile in the Senate, Carl Levin (D., Mich.) offered in June to cut off funds for the ground-based interceptor program that Mr. Bush recently activated in Alaska in anticipation of the North Korean launch. Mr. Levin wants to stop new interceptors from being built, but Senate Republicans wouldn't bring his proposal up for a vote. Mr. Levin has been waging his own private war against missile defenses for a generation, to the point of outflanking Russian objections on the political left.

No missile defense is perfect, but even our current rudimentary shield has proven to be strategically useful these past few weeks. The Navy had at least one ship-based Aegis missile-defense system deployed off the Korean coast, with a potential to shoot down a North Korean missile. The Aegis cruisers have successfully shot down missiles in seven of eight tests in recent years, and could become an important player in protecting allies and U.S. forces against regional missile threats. The U.S. is also dispatching PAC-3s, a more sophisticated version of the Patriot anti-missile system, to Japan. This kind of capability adds to the credibility of the U.S. deterrent, reassures allies and enhances American influence.

Virtually none of this would exist had Democrats succeeded over the years in their many attempts to kill missile defenses. Going back to 1983, Senator Ted Kennedy dismissed Ronald Reagan's Strategic Defense Initiative as a fanciful "Star Wars" program. Ten years later, with President Clinton in office, Democrats starved the program of funds. Republicans made funding defenses part of their Contract with America and spent most of the 1990s battling the Clinton Administration to keep the program alive.

Democrats also made a fetish out of the ABM Treaty, even after the end of the Cold War. Al Gore campaigned to keep it in 2000, promising only to build defenses that would abide by its tight limitations. Senator Biden predicted that dropping out of the treaty to build missile defenses would turn the U.S. into "a kind of bully nation." And Senator John Kerry cautioned that "we must not set aside the logic of deterrence that has kept us safe for 40 years." Neither logic nor deterrence are the first words that come to mind when we think of Mahmoud Ahmadinejad.