The Justices Stand and Applaud - or Don't

AT the State of the Union yesterday, the Justices (the six who were there) stood and clapped when the President expressed appreciation for the military. Otherwise, they sat fand did not clap. I can understand that when the line is, e.g., about passage of the Violence Against Women Act, or gun violence, or raising the minimum wage. But why passivity when the line is about enabling people who work hard to get ahead or opening the door of opportunity to children across America?