Joe Biden became president at one of the most strained moments in US politics. By the time of his inauguration in January 2021, the coronavirus pandemic had killed more than 400,000 Americans and wrecked the economy. Just two weeks before he was sworn in, an angry mob, who were convinced that Donald Trump was the rightful winner of the presidential election, stormed the Capitol to stop the certification of election results. Today, as Biden’s first 100 days in office draw to a close, the new president has already undone much of the previous administration’s contentious efforts. The president has accelerated the country’s vaccination programme, providing economic relief via a $1.9tn Covid-19 aid package and mandating masks in federal buildings. He has also made a handful of environmental announcements, such as re-joining the Paris climate agreement, revoking the Keystone XL oil pipeline permit, pledging to reach net-zero greenhouse emissions by 2050 and decarbonising the power sector by 2035.