washington hillary clinton front-runner race democratic presidential nomination turn monday invitation fox news debate rival bernie sanders california despite agree previously debate may believe hillary clinton time best spend campaign meet directly voters across california prepare general election campaign ensure white house remain democratic hand campaign say statement sanders already agree participate event host fox news follow series heat exchange fifth debate april new york disappoint surprise secretary clinton unwillingness debate large important primary presidential nominate process sanders say statement u.s. senator vermont remain steadfast long-shot battle clinton democratic nomination nov. presidential election although lag delegate count state contest remain naturally fox news disappoint secretary clinton decline debate invitation bill sammon fox news vice president washington manage editor say statement especially give race still contest previously agree final debate california primary california hold primary june 7. clinton turn fox news offer debate sanders