WASHINGTON—Claude Joseph, who has nominally led Haiti as acting prime minister since the July 7 assassination of President Jovenel Moïse, said in a Washington Post interview published on Monday he has agreed to step down, handing power to a challenger backed by the international community. The announcement appears to end a power struggle in the Caribbean nation between Joseph and Ariel Henry, the 71-year old neurosurgeon who was appointed prime minister by Moise two days before the killing but had yet to be sworn in. Moise was fatally shot when attackers armed with assault rifles stormed his private residence in the hills above Port-au-Prince. The assassination has pitched the already troubled nation into chaos, coming amid a surge in gang violence that has displaced thousands of people and hampered economic activity in the poorest country in the Americas. Joseph told The Washington Post that he and Henry had met privately …