This post will be updated as the debate continues. Joe Biden started tonight’s Democratic primary debate with a plea for the 2020 rival who eviscerated him a month ago. “Go easy on me, kid,” the former vice president said to Senator Kamala Harris of California when he greeted her onstage just before the event began. It was a sly bit of gamesmanship from Biden, for he had no intention of going easy on her. Standing next to each other in the center of the stage, the two leading contenders in the second round of the Detroit debate sparred over health care in the opening minutes, as Harris was asked to defend her plan to phase in Medicare for All over a period of 10 years. The CNN moderator Jake Tapper gave Biden an immediate chance to respond, and he jumped at the chance. [ Read: The Democrats’ visceral fear of losing to Donald Trump ] “My response is the senator has had several plans so far, and any time someone tells you you’re going to get something good in 10 years, you should w...