For the world to weather the many gathering storm clouds, the two will have to work together for the next four years.

Yet they got off to a singularly inauspicious start.

Trump may well be the only US president to have suffered a diplomatic defeat before taking office. Violating diplomatic etiquette, the president-elect had inserted himself into active global diplomacy against the policy of the incumbent president. On 23 December 2016, the UN Security Council adopted Resolution 2334 by a vote of 14–0. By abstaining, the Obama administration, in its last significant act at the UN, chose not to veto the resolution’s criticism of unchecked Israeli settlements in occupied lands. As such, Resolution 2334 marked a diplomatic rebuff to Trump, who had lobbied Obama to veto it.

In response, Trump tweeted that the UN is ‘just a club for people to get together, talk and have a good time’. And on 3 January 2017, Alabama congressman Mike Rogers introduced a bill to terminate US membership of the UN that was co-sponsored by conservative-leaning representatives, reinforcing the narrative of threatened US funding cutbacks to multilateral institutions and disengagement from global leadership roles.

Israel’s Prime Minister Benjamin Netanyahu described the US conduct as ‘a shameful ambush at the UN’. President Trump set about rapidly reversing Obama’s approach. On 8 February, Guterres announced the appointment of former Palestinian prime minister Salam Fayyad as special representative to head the Libya mission. The appointment was greenlighted by all Security Council members in discreet soundings, including the United States. But, reflecting opposition from Israel’s Prime Minister, two days later Trump’s new UN Ambassador Nikki Haley created a diplomatic dustup by suddenly announcing US opposition.

A note from Guterres on 11 February emphasised that Fayyad had been appointed based on his personal qualities and individual competence. Guterres also pointed out that no Israeli or Palestinian has so far served in a high UN position.

The United States is just as fiercely opposed to UN efforts to ‘ban the bomb’. In an unclassified NATO document released on 17 October 2016, Washington had urged allies to oppose anticipated UN negotiations. On 27 March 2017, following a vote in the UN General Assembly in December that passed by a solid 113–35 majority (Australia was among the nay-voters), more than 130 countries gathered at the UN to commence negotiations on a ‘legally binding instrument to prohibit nuclear weapons’ — the most significant multilateral development in nuclear arms control in two decades.

In an unprecedented gesture, Ambassador Haley led a 20-strong anti-treaty protest rally outside the General Assembly hall.

In an interview that day, appropriately enough during an AIPAC (the pro-Israel American Israel Public Affairs Committee) conference, Haley boldly declared that ‘they need to know there’s a new sheriff in town’. But the ‘sheriff’ represents a community’s law enforcement officer, not a Mafioso enforcer. In global affairs, the law enforcement authority is the UN Security Council and in choosing to defy the UN, Washington behaves more like an outlaw than a sheriff.

With 193 member states, the UN is unhealthily dependent for 22 per cent of its regular budget and 28 per cent of peacekeeping dues on the US. But the UN is critical to the pursuit of global US interests, and is not just a consumer of US beneficence. The United States may still be the indispensable power but the UN is no less an indispensable international organisation.

As the march of folly into Iraq in 2003 proved, US exercise of power is less effective without UN sanction. Overall, the UN has been attentive to US concerns, interests and preferences. After the terrorist attacks of 9/11, for example, the UN immediately backed the war on terrorism.

Contrary to widespread but erroneous perceptions, the UN is not cost ineffective compared to the United States. A 2006 study by the US Government Accountability Office estimated that ‘it would cost the United States twice as much as the UN to conduct an operation similar to MINUSTAH’ (the UN Stabilisation Mission in Haiti). The difference is attributable to ‘the additional cost of ensuring high US standards for training, troop welfare, and personnel security’.

In a radio interview in 2009, then-US ambassador to the UN Susan Rice noted: ‘If the US was to act on its own — unilaterally — and deploy its own forces in many of these countries, for every dollar that the US would spend, the UN can accomplish the mission for twelve cents’.

Only the UN can set international standards and norms to regulate interstate behaviour. Norms, laws and treaties for governing the global commons are either negotiated in UN forums, or ratified by the UN machinery. The UN Convention on the Law of the Sea and the Comprehensive Nuclear-Test-Ban Treaty are two good examples.

Trump’s first big test where this holds true is North Korea’s nuclear program. Washington cannot be expected to wait until North Korea has acquired a nuclear capability that can target US cities. But unilateral military strikes on North Korea to abort its growing nuclear capability are so formidably difficult as to be ruled out, according to Admiral Dennis Blair, former director of national intelligence.

Instead, like the Iran precedent, some combination of pressure and engagement is needed. On coercion, concerted and mutually reinforcing US, regional (China, Japan and South Korea) and multilateral UN Security Council sanctions will be more effective, more lawful and more internationally legitimate, than just US sanctions.

On engagement, just like in the Iran case, in one form or another the UN will have to be at the table of negotiations and the Security Council’s blessing will be required for any deal that is negotiated. And on top of this, the UN will retain a critical role after any deal with respect to monitoring, verification and, if required, enforcement.

There is no foreseeable substitute for the UN’s institutional and political legitimacy. President Trump and the United States would do well to remember that.

Ramesh Thakur is Professor at the Crawford School of Public Policy, The Australian National University. He is a former UN assistant secretary-general.