In this fascinating history of the American presidency, Cohen, founder and CEO of Jigsaw at Alphabet Inc. and author of books including The New Digital Age and Children of Jihad, chronicles the achievements and legacies of the eight men who have taken that office when the incumbent died. The stories vary widely, starting with John Tyler, who succeeded William Henry Harrison in 1841—becoming both the first unelected president and the first president threatened with impeachment. The transition was more successful for Millard Fillmore, Andrew Johnson, Theodore Roosevelt, Calvin Coolidge, Harry Truman, and Lyndon Johnson. Of this group possibly only Roosevelt would have been elected in his own right, and only Truman, Coolidge, and LBJ were re-elected, like him, but all made a lasting difference to the nation.