Democratic presidential contenders have opened a surprising new front in their effort to retake the White House — calling into question the legacy and leadership of former president Barack Obama, the party’s most beloved leader.

Like young adults seeking to break away from their father’s shadow, the candidates who gathered in Detroit to debate the party’s future this week repeatedly challenged Obama’s record, both directly and indirectly, as too timid, misguided or insufficient for the moral challenge of the moment.

“It looks like one of us has learned the lessons of the past and one of us hasn’t,” said former Obama housing secretary Julián Castro at a key moment in Wednesday’s debate, when he attacked former vice president Joe Biden, with whom he served under the former president, for refusing a more dramatic departure from his immigration approach.

Replacing Obama’s signature accomplishment, the Affordable Care Act, has become the primary policy goal of many of the leading 2020 contenders. Several others have attacked Obama’s efforts to secure a new trade deal with Asia, his decision to surge troops into Afghanistan and the practice of courting wealthy donors, which anchored both of Obama’s campaigns for president.[…]