Donald Trump decided to exit the Paris Agreement because he viewed it as an easy win. With his administration under immense pressure from federal investigators, and some supporters less than pleased with his proposed healthcare bill and intervention in Syria, he snatched one of the last pieces of low-hanging fruit from his withering tree of opportunities.
The Paris Agreement set a global target for reducing greenhouse-gas emissions, intended to prevent the atmosphere from warming by more than 2°C above pre-industrial temperatures. More than 195 countries signed up; the US now joins Syria and Nicaragua as the odd ones out, and the latter didn't sign up because it wanted more aggressive action. Importantly, the treaty is voluntary and allows nations to set their own targets for emission reduction; Trump could have changed US targets without negotiation or exiting the agreement.
The president's controversial decision likely reflects two main factors. Firstly, he either denies climate change outright - Trump has expressed skepticism about global warming on dozens of occasions, and an aide chided a reporter for going off-topic when she asked whether Trump believed in it - or places greater weight on the short-term prosperity of the US fossil-fuel industry than the catastrophic risks of rising global temperatures and sea levels.
Secondly, Trump probably wanted to put a point on the board after a testing few weeks. His travel ban was blocked, he shoved an unpopular healthcare bill through the House that threatens to take healthcare away from 23 million Americans, funding for his border wall with Mexico remains elusive, and the federal investigation into potential collusion between his campaign staff and the Russian government to swing the election has gathered fresh momentum after he fired FBI director James Comey. Leaving the Paris Agreement allowed him to celebrate the fulfilment of another campaign promise, even though the US can't formally withdraw until November 2020.
Trump may genuinely believe the Paris Agreement places a disproportionate financial and economic burden on the US, compared with other signatories such as India and China. The US contributed about $1bn and had earmarked a further $2bn out of a total $10bn fund, and other countries have smaller obligations and less ambitious targets.
America might rejoin if the terms of the deal are improved, Trump suggested. However, his speech about the deal didn't indicate much interest or knowledge of the treaty. It was also biased: it detailed the downsides but downplayed the potential results and ignored the rapid growth of solar, wind and other renewable energy industries in recent years.
Trump, tired of feeling weak and impotent, lunged at the chance to strength his position - against the advice of fellow world leaders, CEOs, close advisers and his own daughter. The sad reality is America's exit from the Paris Agreement won't magically bring back the coal jobs he promised, and threatens to weaken the nation by eliminating its seat at the climate-change negotiating table, discouraging innovation in clean energy, and undermining the world's united efforts to slow climate change. Moreover, it won't distract from the Russia investigation for long, and may well go down in history as Trump's greatest failure.