WASHINGTON — As they filed into the front pews at the National Cathedral, wearing dark suits and mostly solemn faces, one current and four former presidents came together for Jimmy Carter’s funeral. For a service that stretched more than an hour, the feuding, grievances and enmity that had marked their rival campaigns and divergent politics gave way to a reverential moment for one of their own. Barack Obama and Donald Trump, the first two of the group to take their seats Thursday, shook hands and chatted at length. Trump, the former president who will retake the Oval Office in 11