Meanwhile, the EU has reckoned with the profound ill will of the Trump administration. The New York Times this week quoted an EU official who reported that Sondland told a dinner party that he hoped “to destroy the European Union.” In January, the German magazine Der Spiegel published a scathing account of the isolation of Trump’s ambassador among officials in Berlin. He had not made himself any better liked by the time I arrived in September.

At this point, though, it probably matters less that the administration is perceived as obnoxious than that it is perceived as AWOL. As the saying goes, you miss 100 percent of the shots you don’t take. And in the Brexit negotiations, the U.S. has not been taking many shots.

Brexit could mean many different things. There are variations of Brexit that will add more friction to U.K.-EU trade and investment, and variations that will add less. There are variations that minimize potential ill will between the separating parties, and variations likely to maximize ill will. There are variations that do less damage to the future strength and cohesion of the transatlantic alliance, and variations that will do more.

The United States should care. It is the largest investor in the United Kingdom, by far. More trade friction will tend to detract from those investments. Americans hold a considerable share of U.K. public debt. (The U.K. does not break down holdings by nationality, but 25 percent of the total public debt is held overseas.) Those bonds likewise have been devalued by the decline of the pound since the Brexit vote in June 2016. Britain is the fifth-biggest market for U.S. exports. Deterioration of the British economy will impinge on American prosperity too.

These economic concerns are dwarfed by strategic matters. A depressed Britain will field less capable military forces and offer a less helpful partnership to the U.S. around the world. An EU minus Britain is more likely to be protectionist, statist, and neutralist.

You would think the U.S. would be working hard to shape outcomes for the better. You would be wrong.

After a robustly candid discussion in a German-government office three weeks ago, I told the people around the table: “In a way, you should be thankful to President Trump. If literally anybody else were president right now, he or she would be twisting arms to extract a more favorable deal for Britain from the European Union. As is, the British are at your mercy.”

To the extent that Trump and his administration have involved themselves, it has been to urge on the most radical possible Brexit. In November 2018, Trump warned that the withdrawal agreement Theresa May had negotiated with the EU two days earlier would quash U.S.-U.K. trade. “Right now if you look at the deal, [the U.K.] may not be able to trade with us. And that wouldn’t be a good thing. I don’t think they meant that.” Parliament rejected May’s withdrawal agreement in three dramatic votes in January, February, and March 2019, wrecking May’s premiership and forcing her resignation in June.