HOUSTON (AP) – Early front-runner Joe Biden took on the most fire at Thursday’s Democratic presidential debate, and former Obama Housing Secretary Julián Castro was the most explicit in arguing it was time for a new generation. Castro also seemed to allude to speculation about the 76-year-old Biden’s mental acuity during an exchange about health care. When Biden denied that his health plan required people to buy into Medicare, Castro exclaimed, “Are you forgetting what you said two minutes ago?” Sen. Bernie Sanders faced sharp criticism about his universal health care plan from several candidates, and Sen. Elizabeth Warren was more in the background than in prior debates but didn’t damage herself. The likely result is little change in a primary that has been remarkably static for months.