Just 10 candidates qualified for the stage in Houston, but that didn’t change some recurring themes: Joe Biden was again the target of fierce scrutiny, and health care was a central point of contention. But what else did we learn? Guest: Alexander Burns, who covers national politics for The New York Times. For more information on today’s episode, visit nytimes.com/thedaily. Background reading:Attacks on Mr. Biden highlighted the divide over the Obama legacy, with the former vice president repeatedly invoking his old boss’s name.Many Democrats hoped that defeating an unpopular, rampaging president would be relatively simple. But party officials are wary of some potential vulnerabilities that this debate re-emphasized.Here are six takeaways from the contest.