As the confrontation with North Korea heated up, President Obama reversed course on one missile-defense decision, even as he proposed a defense budget that trimmed another half-billion dollars from the enterprise. This self-contradictory behavior on missile defense reflects the president’s ambivalence about a program that he doesn’t want, but knows he needs.

As a candidate, Obama seemed to have no interest in missile defense other than not being outflanked by his opponent on the issue. He signed up to support missile defenses where that “utilizes technology that is both proven and cost-effective.” That proved enough to suggest that he would abandon the concept of missile defense but left a pretty open field for deciding what to do once he got in the Oval Office.

When President Obama settled into the Oval Office, he inherited a program with a pretty clear trajectory. President Bush had already withdrawn from the 1972 Anti-Ballistic Missile Treaty, removing obstacles to testing and deploying robust defenses. The U.S. had already built ground-based interceptor sites in Alaska and California; started building and deploying a network of radar and Aegis-armed missile frigates; inked a deal to deploy ground-based missile defenses in Europe; and launched robust research programs to deal with threats like decoys and attacks by multiple enemy missiles.

President Obama also inherited countervailing voices. Moscow complained that the U.S. missile defense for Europe represented a threat to Russia and an obstacle to a deal on strategic-arms limitations. The president also wanted to tone down the rhetoric with Iran and North Korea, sending signals that the new administration wanted to talk with them. Less missile defense might make the United States seem less threatening, some argued.

Obama was also set to embrace the “Road to Zero,” a vision for ridding the world of nuclear weapons by deemphasizing their importance and reducing arsenals. Proponents of global zero believe missile defenses are destabilizing, motivating others to build more nuclear warheads to overwhelm the defender’s ability to shoot down incoming attacks.

Finally, the president did not want to be seen as a rubber stamp on the military-industrial complex. Since slapping the “Star Wars” label on the program, progressives have always portrayed missile defense as a Reaganite fantasy fueled by wasteful, aggressive militarism. Walking into the job with a Nobel Peace prize to place on the shelf, Mr. Obama was particularly sensitive to any concern that he would continue the “warmongering” of the last administration.

So the new president opted for a minimalist approach. He reduced the overall missile-defense program by about a third, trimming back deployments of ground-based missiles in the U.S. and canceling research and development programs. In 2009, he announced a “phased and adaptive” plan for European missile defense. Purportedly a “new” plan, it was mainly a blueprint for dumping his predecessor’s plan for missile-defense facilities in Poland and the Czech Republic. In 2011, he signed the New START agreement with Moscow, which publically embraced the “Road to Zero” and included promises of “cooperation” on missile-defense issues.

Going into the reelection campaign, the president must have felt he had reached a happy stasis—enough missile defense to show independents and “Reagan Democrats” he wasn’t “weak” on protecting the homeland or kowtowing to the Russians, but not too much missile defense to engender the wrath of his progressive base.

The calculation worked well. Missile defense hardly registered a blip during the campaign—despite continued provocation from North Korea including nuclear and missile tests, the utter failure of engagement with Iran, and the fact that the Russian reset proved an evolutionary dead end.

The problem for the president is that reality keeps intruding into his second term. It is clear that the U.S. missile-defense plans can’t stay ahead of the North Korean threat by simply marching in place. So Obama has had to do more. Recently, the administration announced a reversal of its decision not to deploy additional ground-based interceptors. Additionally, it looks like the administration will cave to Congressional pressure to select an additional missile-defense site in the United States, most likely on the East Coast.

On the other hand, the White House continues to cut back. Last month it officially cancelled the last phase of its “phased and adaptive” plan. And despite continuing setbacks in U.S.-Russian relations, the president is pleading with Moscow to talk about another arms deal. The White House has also proposed trimming more from the Pentagon’s missile-defense budget.

What does it all mean? It appears that the president plans to make few changes to his general approach of doing just enough on missile defense to get by for the next four years. Unfortunately, that timetable puts the president’s policies out synch with missile threats. What the bad guys plan to aim at us is advancing faster than he would like. As a result, when the next presidential campaign rolls around there may be a real “closed missile gap” to worry about.

James Jay Carafano is vice president of defense and foreign policy issues for The Heritage Foundation.