The former White House press secretary’s abrupt political turn comes at a low moment for the Democratic brand.

Fellow members of the Biden administration say she was often an ineffective messenger as press secretary and her book is unhelpful to Democrats trying to rebuild following last year’s election losses.

In a coming book, Ms. Jean-Pierre will describe a “betrayal” by her party when Joseph R. Biden Jr. ended his re-election campaign. Democrats were quick to criticize her.