Barack Obama is the third US president to visit Vietnam since the withdrawal of US troops in 1973. His trip this week is nonetheless replete with historic resonance as Washington consolidates its strategic pivot to Asia and makes common cause with a former wartime enemy against China’s aggressive claims to the South China Sea.

The Vietnamese government hopes that the visit will provide the occasion for a repeal of the US arms embargo, partially eased in 2014 but which remains one of the last vestiges of the war. That could be a step too far.

That Vietnam is seeking closer military co-operation from Washington already carries potent symbolism. It signals the changes taking place as a result of Mr Obama’s determination to devote more of his country’s diplomatic, military and economic resources towards strengthening ties in Asia and countering China’s regional ambitions.