Hillary Clinton watched as the tension in the Hanoi Convention Centre slowly mounted. First, the Vietnamese foreign minister rose to criticise China’s actions in the South China Sea. Then, one by one, other ministers from the Association of Southeast Asian Nations raised similar concerns about Chinese bullying.

Sensing her moment, the US secretary of state asked to speak to the regional summit. For the first time, she announced that Washington had a “national interest” in freedom of navigation and international law in the South China Sea. The Chinese were irate. Yang Jiechi, the foreign minister, looked at Mrs Clinton and warned “outside powers” to stay out of the South China Sea disputes. Turning to the other countries, he fumed: “China is a big country. And you are all small countries. And that is a fact.”

Of the 956,733 miles Mrs Clinton travelled and the 112 countries visited as secretary of state, the 2010 Hanoi meeting was in many ways the defining moment of her tenure. And it provides a valuable glimpse of the worldview that the Democratic nominee would bring to the White House if she wins the November election.