Joe Biden has defied expectations of an unambitious presidency. Domestically, he’s pushed through major legislative packages on building infrastructure and tackling the pandemic. Internationally, he’s led a coalition of democratic countries helping Ukraine fend off Russia’s invasion. On climate change, he’s passed a sweeping law promoting green energy. When he moved into the Oval Office last year, Mr. Biden had a portrait of Franklin Delano Roosevelt hung on the wall across from his desk, signalling his aspirations for a significant expansion of the social safety net and a fight against fascism. But those dreams may soon founder. If the polls…