The highly transmissible delta variant is now the dominant strain of the coronavirus in the United States, the Centers for Disease Control and Prevention reported Tuesday. As of July 3, the latest date for which data was available, the delta variant accounted for 51.7 percent of new Covid-19 cases that had been genetically sequenced in the country. Two weeks earlier, on June 19, the variant accounted for just over 30 percent of new cases. During a news briefing Tuesday, President Joe Biden cited the delta variant's rapid spread to urge people to get vaccinated, "especially young people who may have...