Matthew McConaughey punched a fist down in anger on the lectern of the White House Briefing Room on Tuesday, filling the crowded space with a jarring boom, as he described how authorities in Uvalde, Texas, needed to take DNA from a girl’s green sneakers to confirm her identity amid the carnage.The Hollywood star and Uvalde native showed raw emotion as he addressed reporters two weeks after a gunman killed 19 children and two teachers.