Mr. Johnson and Mrs. May will visit Queen Elizabeth II today to formalize the transition.

With the task of extracting the country from the E.U. now moving into the hands of a Brexit hard-liner and one of the country’s most polarizing politicians, Conservative ministers have begun an exodus from the government.

State of play: The circumstances that brought down Mrs. May haven’t changed — deep divisions within the Conservative Party, which governs Parliament with a tenuous majority, and fierce opposition from other parties to a no-deal Brexit. Here’s how events could unfold.

Another crisis for Britain: Days after Iran seized a British tanker, the country’s foreign minister, Mohammad Javad Zarif, warned that Tehran would protect itself.

Side note: The rise of Mr. Johnson has upended the rules of what leadership should look like, writes our fashion critic Vanessa Friedman.