It is supposed to show that America is back in its own neighbourhood. Yet three weeks before its opening, the Summit of the Americas in Los Angeles threatens to expose Washington’s weakness in the region.

President Andrés Manuel López Obrador of Mexico, the US’s most important ally in Latin America, has dropped a bombshell by vowing not to attend the three-yearly heads of government meeting unless the US invites Cuba, Venezuela and Nicaragua — something the Biden administration had previously ruled out.

Caribbean nations backed López Obrador’s position, as did Bolivia. Brazil’s Jair Bolsonaro has still not decided whether to go and Argentina is wavering. Iván Duque, president of Latin America’s fourth-biggest economy Colombia, could end up being the most important invitee.