(Want to get this briefing by email? Here’s the sign-up.)

Good morning.

Here’s what you need to know:

• “Americans should sleep well at night.”

Secretary of State Rex Tillerson sought to reassure Americans about North Korea today, after a recent exchange of threats between Pyongyang and President Trump.

“Nothing I have seen and nothing I know of would indicate that the situation has dramatically changed in the last 24 hours,” said Mr. Tillerson, who was returning from Asia. He made the comments during a refueling stop in Guam, the U.S. territory that North Korea warned that it might strike.

Tensions with Pyongyang have escalated into perhaps the most serious foreign policy challenge yet for Mr. Trump.