Since at least the time of Abraham Lincoln, US presidential inauguration speeches have contained appeals to unity. Rarely since then has unity been such a central or oft-repeated theme as it was of Joe Biden’s address on Wednesday — but rarely, too, has American democracy felt as fragile as today.

Speaking in the presence of massed security to guard the Capitol from violence but in the absence of massed crowds and of his own predecessor, Mr Biden called for a fresh start. Yet it was a call for a return: to truth and decency, to the respect for liberty, institutions and rule of law that have long been the source of America’s extraordinary dynamism, and its standing in the world.

The tasks of the 46th president differ from those of so many forerunners in their sheer magnitude. Containing a mismanaged pandemic that has cost 400,000 lives and brought economic pain to millions would be hard enough for most presidencies. As Mr Biden acknowledged, the burden of responsibility confronting him is weightier still: to soothe gaping social divisions, repair the American republic, and restore its moral reputation. Those undertakings will long outlast his presidency. How he performs in office will nonetheless determine in no small part whether they can ultimately succeed.