Biden and Warren, longtime frenemies, will finally meet in a debate chasing the biggest prize of all

Vice President Joe Biden came to the Capitol in late 2016 to preside over Senate passage of a cancer-fighting measure named after his son, the Beau Biden Memorial Moonshot. In a day of bipartisan bonhomie, Sen. Elizabeth Warren (D-Mass.) was among those praising Biden, calling him “a man who spent his career fighting for working families.”

But earlier, in a private meeting with Democratic leaders, Warren had slammed the bill that included the Moonshot, saying its relaxed rules on drug companies made Democrats appear cozy with big business — a...