Joe Biden’s first six months have been dramatic. Two-thirds of Americans are at least partially vaccinated. The economy is enjoying its fastest recovery since the 1980s. And, as polls show, the world no longer views America with the dread and pity it felt during the Donald Trump years. This has been the best presidential start in the lifetime of most Americans.

But in politics such runs are the exception. Biden’s coming tribulations — the grinding to a halt of most of his reform bills, the stubbornness of Covid-19 and worries about the murder rate and border crossings — are largely out of his hands. It is easy to forget that Biden looked set to be a lame duck until Democrats won the Georgia special elections in January, giving them control of the Senate. Things could have been so much worse.

Yet Biden is now entering a much tougher phase of his presidency. One of his problems stems from an unforced error — the withdrawal from Afghanistan. It is hard to understand why he felt the need to pull out America’s skeletal force of 2,500 troops before the 20th anniversary of 9/11. The costs of staying are minimal — there has not been a single US combat death in Afghanistan in the past 17 months.