A Palestinian worker carries a bag of flour outside an aid distribution center in Gaza City on April 7. Mohammed Salem/ReutersThe top US humanitarian official said Wednesday it is “credible” to assess that famine is already happening in parts of Gaza.Although US officials have been sounding the alarm about the imminent risk of famine in the enclave, United States Agency for International Development Administrator Samantha Power is the first official to publicly agree with an assessment that famine is already taking place.Power, speaking at a congressional hearing, was asked about an…