This means that the decision of what to do with Darroch, whose post in Washington isn’t due to conclude until the new year, will ultimately fall to whoever succeeds May as prime minister at the end of this month: Boris Johnson or Jeremy Hunt.

It won’t be an easy decision for either man—though Hunt said “if I become PM our Ambassador stays.” To keep Darroch in his post would mean to potentially undermine Britain’s place in Washington at a time where there’s already plenty dividing the two countries. Despite their long-standing defense-and-security partnership, the U.S. and the U.K. are on opposite sides of arguments over Iran (Washington withdrew from the nuclear deal with Tehran, whereas London and its European partners are trying to save it), Huawei (Britain has allowed the Chinese firm to build part of its 5G network despite U.S. security concerns), and climate change (the U.S. abandoned the Paris Agreement, whereas Britain remains committed to it).

Read: The U.S.-U.K. alliance has seen better days

They are even split on issues of British domestic politics. Although a majority of Britons oppose leaving the European Union without a withdrawal agreement, Trump has all but encouraged it—repeatedly criticizing May’s Brexit strategy. He even pledged during his state visit last month to make a “phenomenal” trade deal with Britain once it leaves the bloc—a promise some Brexiteers fear is now at risk if Darroch stays.

The row has already had an impact: On Monday, the White House reportedly disinvited Darroch from a dinner with Treasury Secretary Steve Mnuchin and the emir of Qatar. “If it’s just Trump dealing with Darroch, it’s not as much of a problem because the two of them were not dealing directly with each other anyway,” Amanda Sloat, a former State Department official now with the Washington-based Brookings Institution think tank, told me. “The bigger problem is if word goes out within the administration to senior White House officials and senior State Department officials that they aren’t allowed to engage with Darroch—then that’s really going to handicap his ability to work.”

Still, the optics of firing Darroch and replacing him with someone the White House finds more favorable—such as arch-Brexiteer Nigel Farage, who Trump previously said would do a “great job” as ambassador—could be just as damaging. (Farage said this week that he wouldn’t be the right man for the job.) Rather than conjuring the image of a strong “global Britain” ready to reaffirm its prominence on the world stage once it leaves the EU, firing Darroch would instead portray the U.K. as a weak, deferential actor that can be bullied by even its closest allies.

It would also undermine the process by which Britain appoints ambassadors—one that is based not on the size of campaign donations (as is often the case in the U.S.), but by the length of distinguished service in Britain’s diplomatic corps. Prior to becoming ambassador to the U.S. in 2016, Darroch was the U.K.’s national security adviser.