The pound has sunk to two-year lows, dipping below $1.24 last week, as it has become increasingly likely that Boris Johnson, a hard-line Brexiteer, will be the one to navigate Britain’s departure from the E.U. Some fear Brexit could set off economic chaos, deal or no deal.

Mr. Johnson would also have to face another complication: Jo Swinson, a 39-year-old Scottish lawmaker, who on Monday took over leadership of the Liberal Democrats, a party that opposes Brexit. She could become a kingmaker in the coming months as the Conservatives try to tackle Brexit with a razor-thin majority in Parliament.

The Daily: Our latest episode is about how Mr. Johnson made Brexit and how Brexit is now making him prime minister.

In Spain: Pedro Sánchez and his Socialist party, whose victory in April was a rare vote of confidence in the E.U., are struggling to assemble a governing coalition. In a speech, Mr. Sánchez said the constitution should be changed to make it easier to form a government and avoid plunging the nation into another lengthy political deadlock.