The challenge for King Charles III as he embarks on this week's state visit to the U.S. is, as always, to live up to his mother’s example. The late Queen Elizabeth II wowed Congress in 1991 with a speech that celebrated the shared democratic traditions of Britain and the United States, quoted Abraham Lincoln, Franklin D. Roosevelt and Ralph Waldo Emerson, and highlighted the deep bonds between the two nations. Those themes will also be at the top of Charles’ agenda as he celebrates America's 250th birthday and seeks to calm tensions surrounding Prime Minister Keir Starmer’s refusal to support U.S. President Donald Trump’s war against Iran , said Douglas Brinkley , a presidential historian at Rice University in Texas. “We’ve got to always make the distinction that there’s a difference between the government of the U.K. and the kings and queens of Great Britain, who are really always coming to try to put (on) a good face,” Brinkley told The Associated Press.…