The Democrats who want to be president can’t quite figure out how to talk about the most popular figure in their party. Former president Barack Obama casts a long shadow over the 2020 primary campaign: Preserving Obama’s legacy is the heart of former vice president Joe Biden’s pitch to voters — which has allowed his rivals to mark him as complacent. More left-leaning candidates, such as Sen. Elizabeth Warren (Mass.), say the next president needs to do more to push for health-care reforms and combat income inequality — but lately, she’s struggling to sell her proposals. Onetime Obama Cabinet secretary Julián Castro has ripped his former boss’s record on immigration and deportation. Meanwhile, South Bend, Ind., Mayor Pete Buttigieg raced to have a reporter correct a story that misquoted him citing “failures of the Obama era.” Sen. Kamala Harris (Calif.) said in Wednesday’s debate that it’s crucial to “rebuild the Obama coalition” because “that’s the last time we won.” Picking and choosing which parts of Obama’s tenure to embrace, and how firmly to embrace them, has become a delicate game in the primary season.