In today's edition, we’ll explore shifting attitudes on immigration, the inspiring journey of a Sudanese refugee, the challenges facing Democrats vying for Latino votes, central European efforts to boost birthrates, and how humorist James Thurber was shaped by his hometown.

But first, diplomacy, by its nature, must be discreet to be effective. So when confidential cables from the British ambassador in Washington were leaked last weekend – revealing his unflattering views of the Trump administration – Sir Kim Darroch had little choice but to resign. Especially when Donald Trump tweeted, “We will no longer deal with him.”

He might have soldiered on till his retirement at year’s end, but what tipped the scales, it seems, was Boris Johnson’s refusal to back the ambassador during a televised debate. Mr. Johnson is widely tipped to become Britain’s next prime minister. He is also a champion of Brexit, pledging to take the United Kingdom out of the European Union next October, deal or no deal.

That policy, which would cut London adrift from the duty-free EU trade network, means Britain will be in urgent need of trade deals with other powers; the United States is top of Mr. Johnson’s list, though U.S. officials have indicated they intend to strike a hard bargain.

Could it be Mr. Johnson judged it politic to stay in President Trump’s good books for the sake of a trade agreement, even at the price of having “thrown our top ambassador under the bus,” as one British cabinet member put it?

Whatever his motives, this week’s events have thrown into stark relief just how many challenges Mr. Johnson will face, if indeed he becomes prime minister, as he tries to steer a new course for the United Kingdom.