In interviews, several family members of Covid-19 victims said it was difficult to hear Mr. Biden suggest that the nation was returning to normal while they were still grieving. “There’s no return to normalcy for us,” said Sabila Khan, 42, of Jersey City, N.J., who created a Facebook support group after her father died of Covid-19. “It’s very nerve-racking when the government is encouraging you to just move beyond it. We lost our loved ones. We are never moving past this.”... But the absence of a vaccination requirement for White House party guests is also evidence of the challenges ahead, said Dr. Thomas Frieden, a former director of the Centers for Disease Control and Prevention. “There is so much toxic politics around Covid that it’s constraining sensible action,” he said. “Obviously it makes sense to require proof of vaccination in various settings, but that has become a political lightning rod.”