Think back five years — challenging, we know, given all that’s transpired since then — but Joe Biden at the time seriously considered whether to declare he would serve just one term if elected president of the United States. It was late 2019, and he was struggling to gain traction in a crowded Democratic primary field and needing to set himself apart from his younger rivals. We know now he made no such pledge and won the prize anyway. But the belief lingered well past his defeat of Donald Trump in 2020 that, once his term ended, he could well cede the mantle of Democratic Party leader, given h...