Defiance and caution from Kim Jong-un

North Korea’s leader vowed on Wednesday to expand his country’s nuclear force and threatened to show off a “new strategic weapon.” He also warned that North Korea would no longer be bound by a self-imposed moratorium on tests of nuclear and long-range ballistic missiles.

But his threats lacked specifics, and he didn’t explicitly say that he was terminating diplomacy with the U.S., reflecting a wait-and-see approach that leaves room for more negotiations.

News analysis: “Both the Iranians and the North Koreans seem to sense the vulnerability of a president under impeachment and facing re-election, even if they are often clumsy as they try to play those events to their advantage.” Read more from our national security correspondent.

Unexplained drones swarm over the prairie

Since mid-December, sheriff’s departments in eastern Colorado and western Nebraska have received reports of drones flying in precise formations over rural towns and open fields at night.

The drones have prompted a federal investigation — and may be perfectly legal — but they remain unexplained. Some have suggested that they might be part of a mapping operation or a land survey conducted by an oil and gas company.

Background: Operators of all but the smallest drones have been required to register with the federal government since 2015, but state and local officials aren’t able to easily identify a drone’s owner or to track its location.