"The US says that its policy favouring the status quo on Taiwan has not changed. But Trump is famously flaky on Taiwan," notes Tisdall.

He frequently makes contradictory, sometimes alarming statements. Discussing Xi's intentions, he said recently that any move to invade was "up to him" " a choice of words that suggests he does not care much either way, even if he did add that he would be "very unhappy" were China to invade.

Summit bottom line: will a weakened, outmanoeuvred Trump cut back US support for Taipei in return for Xi's help with Iran and favourable deals on, say, rare-earth minerals and agricultural imports? Serious questions similarly surround the depth of Trump's commitment to South Korea and Japan " Beijing-Tokyo tensions are running hot at present, partly because of Taiwan; and his ability to persuade China to rein in North Korea, a hostile, bullish rogue state that, unlike Iran, really does possess nuclear weapons.