PHILADELPHIA — Breakfast started with an apology, but Democratic Party leaders’ attempts to make peace with Bernie Sanders supporters who were excluded from the traditional convention roll call fell short of healing divisions in the Iowa delegation that were on full display Wednesday morning. R.T. Rybak, a vice chairman of the Democratic National Committee, offered a “formal apology” for the content of leaked emails written by committee staffer “who didn’t follow the strict, strict mandate to stay neutral.” “We betrayed your trust,” Rybak said at the Iowa delegation’s daily breakfast meeting.