LAVEEN VILLAGE, Ariz. — President Joe Biden on Friday formally apologized to Native Americans for the “sin” of a government-run boarding school system that for decades forcibly separated children from their parents, calling it a “blot on American history” in his first presidential visit to Indian Country. “It’s a sin on our soul,” said Biden, his voice full of anger and emotion, during his visit to the Gila River Indian Community’s land on the outskirts of Phoenix’s metro area.