Four decades ago, Phillip Schuller stumbled into history, joining a demonstration that involved an ex-priest, 10 pints of blood and Donald H. Rumsfeld’s front lawn. Schuller’s 1976 arrest ultimately upended Maryland’s law banning protests outside private residences. And it’s a key reason why, today, abortion rights activists can picket in front of the suburban Maryland homes of conservative Supreme Court justices. “It’s correct to say that thanks to him, they’re not getting arrested,” said David Rocah, a senior staff attorney with the American Civil Liberties Union of Maryland.