President Obama returns to the Oval Office from the Rose Garden on Thursday after announcing a breakthrough in nuclear talks with Iran. (Pablo Martinez Monsivais/AP)
By Dan Balz, Chief Correspondent
April 4, 2015 at 2:35 PM
It is perhaps only an accident of history that three of the key actors in the diplomatic efforts to deny Iran a nuclear bomb are the 2004, 2008, 2012 and probable 2016 Democratic presidential nominees. But their intertwined ambitions provide a dramatic backdrop to the unfolding and unfinished story.