He’s compared himself to Abraham Lincoln and Teddy Roosevelt, evoked nostalgia for John F. Kennedy, sought to emulate Ronald Reagan, (belatedly) praised George W. Bush, and enlisted the assistance of Bill Clinton in his 2012 re-election effort, but as his second term stumbles along, the president with whom Barack Obama finds himself being compared is Richard M. Nixon. My father, Lou Cannon, covered the White House with distinction for the Washington Post for many years, beginning in the Nixon administration. He employed an easy rule of thumb when fielding phone calls from anonymous tipsters: If the caller said, “I have...