Europeans, if they can bear to watch, are observing US politics with a mixture of fascination and horror – and it’s all down to Donald Trump. Each week seems to bring another democracy-shattering rumpus, scandalous revelation or shocking tweet. The depth and evident bitterness of America’s public divisions are unsettling for friends and allies who count on dependable US leadership.

It is hard to overstate how badly Trump has hurt America’s worldwide reputation. US presidents have been internationally unpopular before – George W Bush over Iraq, for example, or LBJ over Vietnam. But Trump has sunk to an all-time low.

Opinion surveys reveal the negative impact on US global standing. A 25-nation Pew survey last year found, overall, that 70% of respondents had no confidence in Trump’s leadership. While a majority still held a favourable view of the US, unfavourable views were up sharply from the Obama era. About 70% said the US under Trump did not take sufficient account of the interests of other countries and was doing less to address international problems.

Trump won’t be around forever. But this collapse in trust may have lasting, long-term implications for transatlantic ties. A survey of 60,000 people in 14 EU member states published this fall by the European Council on Foreign Relations found most Europeans “no longer believe the US can serve as a guarantor of their security”. Europe and America risk drifting even further apart in 2020.

Not all this angst can be laid at Trump’s door. But his personal hostility to the EU and individual European leaders, his denigration of Nato, his bypassing of his own intelligence agencies and state department, his collaboration with Russia’s Vladimir Putin, and his willingness to betray staunch allies such as Syria’s Kurds are undoubtedly stoking fears about US reliability in security matters. Trump’s hope of scoring a big pre-election foreign policy “success” adds to the general nervousness.

Some of these fears are structural. Europeans, including Britons, are alarmed by Trump’s disdain for the UN and other multilateral decision-making bodies, and his readiness to ignore international treaties. His go-it-alone chauvinism weakens US leverage. It also shows ingrained disrespect for the global rules-based order that has sustained western liberal democracy in the postwar era.

Trump’s admiration for authoritarian regimes and “strongman” leaders such as Putin and China’s Xi Jinping, when set alongside his electoral shenanigans at home, has strengthened the view that he is no friend to democracy – at a time when democracies everywhere are under sustained attack.

The US under Trump’s baleful tutelage is not only losing influence and respect. It is also, increasingly, a source of and contributor to global woes and instabilities. His unilateral, nationalistic, self-defeating approach threatens deepening trouble across the board next year.

How much longer Nato can last as a coherent force, given Trump’s relentless antipathy, is an open question

Unresolved issues around Iran’s and North Korea’s nuclear ambitions are one obvious 2020 flashpoint. Trump’s interventions to date have made matters worse. Now mounting anger and frustration in both countries could bring tensions to a head. In Iran’s case, such escalation may quickly draw in Saudi Arabia and Israel – and Turkey too, given Trump’s craven appeasement of Ankara after its invasion of Syria.

How much longer Nato can last as a coherent force, given Trump’s relentless antipathy, is an open question. It is one Russia will be constantly testing as it expands its influence in the Middle East, builds up its conventional and nuclear forces, and intimidates neighbors such as Ukraine and the Baltic states.

Another fraught 2020 issue is whether a worldwide recession can be avoided as Trump pursues his trade vendetta with China, market confidence falls and debt levels (including the projected $1tn 2020 US deficit) rise. Judging by his recent belligerence, Mike Pompeo, America’s undiplomatic chief diplomat, appears determined to trigger a new cold war with Beijing. Harsh words could easily turn to blows over Hong Kong, Taiwan and the South China Sea.

Yet more pressing still, in the wake of Trump’s renunciation of the Paris climate accord, is genuinely urgent action to tackle the environmental crisis engulfing the planet, evidenced most recently by record floods in Britain, lethal wildfires in California and Australia and the ongoing mass extinction of species from the Arctic to the Amazon.

In short, Trump has an awful lot to answer for in 2020. America’s friends fervently hope America’s voters make America great again – by agreeing to dump Trump. Think of it as your gift to the world.