As soon as the plan was published, senior officials in Brussels could see that their boss had made a terrible mistake.

They understood the rationale for vaccine restrictions on shots shipped from the European Union, but they could hardly believe that Ursula von der Leyen had missed the bigger picture and how the proposals would land in Ireland.

The European Commission president had been among those insisting through four years of Brexit negotiations that Irish border checks could jeopardize the island’s peace settlement. Less than a month after the trade deal with the U.K. went into effect, the EU was now the one threatening to put up barriers and unilaterally trigger emergency clauses in its accord with the U.K.