Daniel DePetris explains why attacking North Korea would be extremely dangerous:

During a Senate Armed Services Committee hearing in December, Graham revealed that he will be introducing an authorization for the use of military force to provide the president with the statutory approval to preemptively stop Pyongyang from finishing the development of its ICBM. Republican majority leader Mitch McConnell should simply ignore it. And if the GOP brings it up for a floor debate, Senate Democrats should do everything in their power to prevent such a resolution from passing. A preemptive strike on North Korea would be an unmitigated disaster—a military action that is much more likely to escalate into a full-blown regional confrontation with a million-man North Korean army than force Kim to tremble in his basement.

There’s no question that attacking a North Korean missile launch would be a terrible idea for many of the same reasons that other proposed attacks on North Korea would be insane. It would potentially expose South Korea and U.S. forces to retaliatory strikes, and even if it “worked” as intended it would only convince their government that they should keep working on their missile projects. In the unlikely event that an attack on North Korea didn’t immediately lead to a resumption of hostilities on the peninsula, it would only encourage their government to intensify all of the efforts that we want them to give up. It would be the perfect example of a short-sighted, counterproductive, and irresponsible use of force, so naturally the perennial warmonger Lindsey Graham was the one to propose it.

I would add that it wouldn’t even be a “preemptive” attack. It wouldn’t be an attempt to forestall a North Korean attack on us, but would be and would be perceived as an aggressive act. It would contribute significantly to a souring of relations with China, and it would make Beijing much less interested in cooperating with our government in pressuring North Korea. Any benefit gained by setting back North Korea’s missile program for a short time would be heavily outweighed by the costs.