Donald Trump and Xi Jinping are likely to discuss many issues as they meet this week in Beijing. But alongside trade, technology and the war in Iran, one topic of conversation will stand out – the future of Taiwan.

Taiwan has long been a sensitive issue in Sino-American relations. Beijing regards the island as a breakaway province which must be reunited with the mainland. The United States has long opposed such a step. Yet in recent months, Trump has fuelled speculation that he may be ready to change key aspects of US policy on the issue, potentially granting Beijing long-sought concessions.

Trump’s apparent readiness to make these moves means that Taiwan is one of the issues on which we might see the most significant policy developments at the summit. And that could happen simply through the famously voluble president uttering just a few simple words.

The president’s policy towards Taiwan has been inconsistent and seemingly more malleable than that of previous administrations. Advocates for Taiwan point out that his administration recently approved the largest ever US arms sale to the island. But at the same time, he has sowed doubts about the strength of his support for Taiwan’s independence.

US policy towards Taiwan has traditionally been based on two principles. The first is “strategic ambiguity”, which means that the US declines to explicitly state whether it would actively use its military to defend Taiwan from attack by China. This policy is supposed to deter China while also discouraging Taiwan from formally declaring its independence from Beijing.

The second principle is the “one China policy”. According to this policy, the US recognises Beijing as the legitimate government of China, while opposing any violent solution to its dispute with Taiwan. It also retains robust informal links to the Taiwanese government in Taipei.

Observers are concerned that Trump may water down these principles during his summit with Xi. For instance, he might state that the US not only “does not support” Taiwanese independence but actively “opposes” it. Or he might double down on previous comments he has made indicating that whether or not Xi invades Taiwan is “up to him”.

Trump has also explicitly stated that he will discuss future US arms sales to Taiwan with Xi during this week’s summit. This violates one of the so-called Six Assurances that the US has upheld towards Taiwan since the 1980s, and which were endorsed by the US Congress in 2016.

Even securing a discussion of arms sales would be a victory for Xi, who would welcome an opportunity to chip away at the Six Assurances. Presumably he would then try to weaken the US commitment to the other five, which include a US commitment not to change its position on Taiwan’s sovereignty.

More concretely, if Xi succeeds in making US arms sales to Taiwan a legitimate topic of negotiation in Sino-American relations, then he could head them off in the future by offering the US concessions in other areas. For instance, if Trump or a future president asks Beijing for its help settling a conflict like that in Iran, Beijing might demand an end to US arms sales to Taiwan as the price.

High stakes

Given Trump’s reputation as a formidable China hawk, his attitude towards Taiwan may seem surprising. But it’s actually part of a longstanding pattern.

In relations with China, Trump has arguably always prioritised economic issues, while appearing less concerned about the security of America’s regional allies. He has also raised doubts about whether Taiwan is even defensible. In his first term, he reportedly told aides that: “Taiwan is like two feet from China. We are 8,000 miles away. If they invade, there isn’t a fucking thing we can do about it”.

Trump is also both highly transactional and less focused on abstract principles of foreign policy than most previous presidents. He views America’s support of allies such as Taiwan as a gift that it gives them, one that is often not worth the cost. If he can achieve a concrete victory for himself today by trading away support for Taiwan tomorrow, he may well be willing to do so.

All of these developments matter because they make a violent conflict between China and Taiwan, potentially ultimately involving the US, more likely. If Trump makes concessions to Xi, it will be the latest signal that US support for Taiwan is wavering. That made be read in Beijing as permission to violently change the status quo. Even though such an act might belatedly then be met with force from Washington in response, it is made more likely by Trump’s stance today.

Even worse for Trump, the summit comes at a time when American power and the wisdom of its long-term strategy are being visibly called into question in the Middle East. The US is bogged down in an intractable conflict and has severely damaged its deterrent capacity in the Indo-Pacific by burning through advanced munitions at a high rate. Trump’s personal unpopularity is also rising at home amid the war and its economic fallout.

This weakened position makes it even more likely that Trump will want to strike a deal with Xi to help end the war in Iran or ease trade tensions to help the economy at home. Taiwan may be the price of that – and, ultimately, peace.

Andrew Gawthorpe is affiliated with the Foreign Policy Centre in London.

Operation Epic Fury is over. Or at least, that’s what the US secretary of state, Marco Rubio, announced on May 5, describing any further US action in the Gulf as purely “defensive”.

Rubio’s insistence that the conflict the US and Israel launched on February 28 achieved its objectives is open for debate. But this change of tone and terminology is likely to reflect arguments that raged in the US Congress as the war approached the two-month mark at the end of April, about whether the Trump administration must seek congressional approval for the conflict as required by US law.

The conflict has become the latest episode in a long struggle between the US Congress and the presidency over which branch of government can legitimately start wars. And, in a surprising way, Donald Trump’s actions seem to be pushing power back towards Congress.

The US constitution splits war powers between the presidency and Congress. It gives Congress the power to raise armies and declare war but makes the president the commander-in-chief of the military. That means that, in theory, you need to get Congress to agree to fund and start a war and the president to agree to wage it.

Since the second world war, this system has been changing. The last time the US formally declared war was in 1942 against Bulgaria, Hungary and Romania – having already declared war on Japan and Germany in December 1941. Since then, presidents have often plunged the country into hostilities on their own authority without getting a declaration of war from Congress.

Congress still needs to fund the military – but, with very few exceptions, the legislature has always done so. Individual members of Congress have generally been happy to let presidents take on the blame for starting wars. After conflicts have started, legislators have been unwilling to cut off funds for the troops in the field. As a result, Congress has given up much of its influence over decisions of war and peace.

Read more: Trump sidelined Congress’ authority over war on Iran – and lawmakers allowed it, extending a 75-year trend

But not entirely. The high point of Congressional pushback was in 1973, during the tail end of the Vietnam war, which by then had become extremely unpopular. In this context, Congress challenged the executive branch by passing the 1973 War Powers Resolution (also known as the War Powers Act). It’s this law that is shaping the debate over Iran today.

The War Powers Resolution basically repeats what the constitution says: that Congress has to start wars, but it allows for some flexibility. If there is a surprise attack on US forces, the president can act to repel that attack for 60 days before getting a declaration of war from Congress.

As reasonable as this may sound, every administration since the War Powers Resolution was passed has questioned its constitutionality and refused to be bound by it.

To be sure, some presidents have asked Congress for a statement of political support before launching a major war, as they also had done before the War Powers Resolution was passed. For instance, George H.W. Bush did so before the Gulf war of 1990-91. But when doing so, presidents have generally maintained that they did so purely to ensure national unity, and not because the War Powers Resolution required it of them.

Presidents have also launched many interventions in which they ignored the resolution entirely – as Bush himself did in Panama in 1989.

Unpopular war

As a result, the resolution has never acted as a meaningful constraint on presidential war-making power. But things may be changing. The war in Iran is so unpopular that Congress asserting its authority over war powers more strongly than any time since the War Powers Resolution was passed. In the process, it is turning the resolution into something that might meaningfully affect the course of the war.

One reason for this is that even Trump’s Republican supporters in Congress are aware of how unpopular this war is. Many are worried about losing their seats in the midterms later this year. As a result, Congress is stirring. Even senior Republican figures are treating the War Powers Resolution and its 60-day clock as an important constraint on the administration and demanding that the war stop or be authorised by Congress after it passes that mark.

In response to this political pressure, the Trump administration seems to be paying more attention to the requirements of the War Powers Resolution than most administrations before it.

The White House is too afraid of Republican opposition to ignore the resolution entirely, particularly when it knows that it may soon have to ask Congress for more funding for the war. Even the argument it made that the 60-day clock has paused during the ceasefire is an indication that it sees the clock as a legitimate thing in the first place.

If the war starts up again, Republicans will clamour for the administration to come to Congress for a declaration. This would probably trigger a major debate over the conditions that Congress wants to attach regarding strategy, goals and funding.

What this shows is that many of the checks and balances of the constitution only work when there is the political will to make them work.

Andrew Gawthorpe is affiliated with the Foreign Policy Centre in London.