North Korea defiantly celebrated its fifth nuclear test Friday, claiming that it can now make warheads small enough to fit onto a missile and warning its “enemies” — specifically the United States — that it has the ability to counter any attack.

Although the North’s proclaimed advancements could not be verified — and Pyongyang has a track record of exaggeration — the test appeared to mark another step toward North Korea’s goal of putting a nuclear warhead on a weapon capable of reaching the mainland United States.

Friday’s test — the North’s second this year — underscored the ability of Kim Jong Un’s regime to make progress on its nuclear and missile programs despite waves of international sanctions and isolation. […]