Has North Korea achieved the nuclear weapons capability it thinks it needs to defend itself against the United States? Its latest and most advanced intercontinental ballistic missile test was undeniably hostile. Yet, paradoxically, it could signal a chance for a new diplomatic opening.

There are many reasons to be skeptical of the North and pessimistic about the prospects for solving the crisis over its nuclear program, given the ruthlessness of its leader, Kim Jong-un, President Trump’s bombast and the deep mistrust between the two countries. But with regional tensions and the risk of miscalculation so acute, the United States and others, including China, Russia, South Korea and Japan, need to exhaust all avenues in the search for ways to limit the North Korean program.

North Korea says its goal is a missile-delivered nuclear weapon capable of striking the United States. It considers itself a nuclear power, with an arsenal of 20 or more weapons, that its officials say is designed to keep the United States from invading and to force an end to sanctions.

Mr. Kim has greatly accelerated the nuclear program. The country’s sixth nuclear test came in September and its third test of an intercontinental ballistic missile on Tuesday. Some experts doubt whether the Hwasong-15 missile can deliver a nuclear weapon, but it flew higher and longer than previous missiles and was judged capable of hitting Washington. Mr. Kim called the test a “resounding success” and “the accomplishment of the historic cause of the national nuclear program, the cause of building a missile power.”