london/washington u.s. democratic presidential front-runner hillary clinton want britain stay european union campaign say saturday follow intervention u.s. president barack obama urge britons vote remain hillary clinton believe transatlantic cooperation essential cooperation strong europe unite always value strong unite kingdom strong eu value strong british voice eu clinton senior policy adviser jake sullivan say statement provide reuters clinton spend four years u.s. secretary state obama first term make foreign policy credentials central piece campaign president november 2016 race white house clinton position eu first report britain observer newspaper obama leave britain sunday spark row three-day trip bluntly tell britain remain european union preserve remain global clout anger critics eu friday warn britain would back queue trade deal leave club one strong u.s. interventions affairs western european democracy since cold war hillary clinton also want britain stay eu