The protests pose two political dangers to Biden. They could exacerbate his estrangement with the left wing of his party, particularly among young people who are a key constituency for his re-election chances. And they could feed into the Republican narrative that Biden, not the volatile former president, Donald Trump, has presided over disarray at home and abroad, which could alienate middle-of-the-road swing voters. Biden’s standing among voters under 30 has eroded dramatically from four years ago. According to a Harvard Youth Poll released in April, Biden leads in that age group with 45 per cent to Trump’s 37 per...