Like an out-of-control wrecking ball, swinging wildly back and forth, Donald Trump smashes up the international order without much thought for the consequences. Lacking coherent strategies, workable plans or consistent aims, he power-trips erratically from one fragile region, tense warzone and complex geopolitical situation to another, leaving misery, confusion and rubble in his wake. Typically, he claims a bogus victory, demands that others repair the damage and pick up the tab, then looks around for something new to break.

The president will bulldoze into another international minefield this week – the fraught standoff between China and Taiwan – when he travels to Beijing for a two-day summit with President Xi Jinping. After a string of humiliating policy implosions over Ukraine, Gaza, Nato, Greenland, and now Iran and Lebanon, needy Trump craves a diplomatic success to flaunt at home. But his hopes of vote-winning trade pacts are overshadowed by his latest war of choice. He needs Xi’s promise not to arm Iran if all-out fighting resumes – and Xi’s help keeping the strait of Hormuz open as part of a mooted framework peace deal.

The weakness of Trump’s position going into the summit is fuelling speculation that reduced US support for Taiwan may be Xi’s price for playing nice. Xi knows the Iran war is deeply unpopular with US voters. Trump is universally blamed for pushing up global energy, food and medicine prices. European allies have refused to bail him out, Russia is undeservedly benefiting from inflated oil prices – and poorer countries bear the brunt. Trump is not winning militarily, either, as shown by his half-baked, on-off Project Freedom. He’s desperate to escape the quagmire he created – and reduce Xi’s advantage.

What will Xi make of his epically furious guest? For China, Trump is the gift that keeps on giving. Thanks to him, the US is increasingly viewed internationally as an aggressive potential enemy or unreliable friend, much given over to treachery. Its loss of influence and leverage is Beijing’s gain: Trump’s volatility assists Xi’s promotion of China as the new guardian of global stability. The Iran impasse is drawing US forces away from Asia – it now has two aircraft carrier strike groups in the Middle East – and reducing its military capacity to defend Taiwan and regional allies from future Chinese aggression.

The downside for Xi is the negative impact of the war on energy prices, global trade and export demand at a time when China’s economy is already struggling. Last year, about 80% of Iranian oil shipments were bought by China – shipments the US navy is now blocking. So far, Beijing has largely managed to offset supply shortfalls from the Gulf by drawing on reserves, capitalising on green energy and buying more oil from countries such as Brazil and Russia. But for the world’s largest importer of crude oil, safe and reliable navigation through the strait of Hormuz is critical.

China is urging both sides to embrace a negotiated settlement. It hosted direct talks last week with Iran’s foreign minister, Abbas Araghchi, and is backing Pakistani intermediaries. Recalling China’s successful 2023 fence-mending between Saudi Arabia and Tehran, anxious Gulf states are counting, like Trump, on Beijing’s ability to influence its Iranian ally, with which it launched a “comprehensive strategic partnership” in 2021. And Xi is unafraid to take on Trump. He warned recently against a return to “the law of the jungle”. He added: “To maintain the authority of international rule of law, we cannot use it when it suits us and abandon it when it doesn’t.” Ouch.

The wishful idea, voiced in Washington, that the brazen US-Israel aggression against Iran has shaken Xi into cooperating, and will deter Beijing’s expansionist ambitions in Taiwan and the South China Sea, would be more convincing if the war had actually succeeded. Instead, Trump has exposed the limitations of US power, military and political, and revealed a startling lack of strategic understanding. While he prefers a peaceful outcome, Xi’s top priority is not going to be digging Trump out of a hole in the Middle East. And if he chooses, he has the means to prolong the US nightmare by expanding deniable military support for Iran – as he has done for Russia in Ukraine.

Trump seems aware of this risk. He wrote to Xi last month, asking him not to supply weaponry to Tehran – and said he had received assurances China would not do so. But the Foundation for Defense of Democracies, a conservative US research institute, claims China already provides Iran with dual-use precursor chemicals for its ballistic missiles, satellite intelligence about US military movements, assets and bases, and help with sanctions evasion and money laundering. It’s possible that more, overtly military aid could flow to Tehran if Trump starts bombing again or fails to satisfy Xi in their summit talks.

For a man who likes to boast he holds all the cards, the US president may find himself seriously short of trumps when he sits down with Xi. It’s an instructive measure of the geopolitical omnishambles Trump has created. His own 2026 national defence strategy states that deterring China in the Indo-Pacific is of primary importance. Yet Trump has hopelessly compromised the US position with his Middle East obsessions and biases. Typically, others could now take the fall for his incompetence. Which is why Taiwan – and US allies such as Japan, South Korea and the Philippines – might be worried.

Xi’s top external priority is not the Middle East. It is the unification of communist China with a de facto independent, democratic Taiwan – a personal legacy project that he has repeatedly threatened to pursue by force. Pentagon planners believe China’s ever-expanding military could be ready to launch an invasion next year. Taiwan’s forces are vastly outnumbered, while its fractious political parties are as divided as ever about increased defence spending and the wisdom or not of seeking closer ties with Beijing.

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

In other words, will Trump claim another fraudulent triumph on the world stage in Beijing while selling out US allies, kowtowing, once again, to an anti-democratic, anti-western dictator, and recklessly demolishing decades of painstaking diplomacy that, until now, has prevented a war in the Pacific over Taiwan? This week, largely due to wrecker Trump, the writing is on the wall for the future of the US as number one global superpower. With all his blundering, this know-nothing numbskull has put China in the driving seat.

• Simon Tisdall is a Guardian foreign affairs commentator