Democratic presidential nominee Joe Biden’s new openness to liberal priorities such as eliminating the legislative filibuster and packing the Supreme Court raise fresh questions about how durable his centrism and institutionalism will be once under pressure from his left flank on Capitol Hill.

Biden won the Democratic primaries by ignoring the online Left and steamrolling the progressive supporters of socialist Bernie Sanders. Alexandria Ocasio-Cortez, the New York Democratic congresswoman who has become a liberal sensation, played a smaller role in the convention that nominated him than longtime Republicans like John Kasich. The former vice president weathered riots that once appeared to be a threat to his campaign by traveling to Kenosha, Wisconsin, denouncing the violence, and distancing himself from defunding the police.