It has been roughly 1,100 days since Barack Obama was president, a number that means different things to different people — be they Democrats, Republicans or readers of any party. Like so many of his predecessors, Obama signed up to write a presidential memoir, but he is running late, at least by the standards of the genre.His publisher has yet to announce a title or even a publication date. George W. Bush’s Decision Points, by contrast, came out roughly 600 days after he left office.There have been presidential autobiographies for nearly as long as there have been American presidents. Four of the first five chief executives tried to write their life stories, with Washington the only holdout. But political memoirs create a peculiar set of problems for their authors.Two hundred years of history make the temptation clear: to emphasise the politics at the expense of the memoir. But that history also provides some useful tips if Obama and other political memoirists will consider them.Washington’s characteristic reticence left John Adams to go first. His book, which he began not long after Thomas Jefferson defeated him in the 1800 election, offers the first lesson for Obama: personal writing doesn’t mean you have to focus on personal grievances. Adams intended his book for posthumous publication, but his voice was snappy and lively, a quality Obama might aspire to. Still, Adams frequently squandered it on arguments with his former rivals.Instead of describing the Revolutionary War, for instance, he got distracted by attacking Alexander Hamilton and Thomas Paine. The former president picked fights for more than 400 pages. He never finished his book.Over the next few decades, a handful of presidents joined the founders in attempting autobiographies, but they each ended up with a text that was grumpy, defensive and incomplete. The Civil War changed that — the incomplete part, at least.After leaving the White House in 1861, James Buchanan searched for an author to answer his many detractors. (Slamming the former president had become a rare activity that united North and South.)Eventually, he finished the book on his own, blaming the war on abolitionists, reporters, generals — on everyone, in short, but himself.Buchanan’s memoir astonished readers, by appearing so quickly and also by being terrible. “Instead of trusting his enemy to write a book,” The New York Times marvelled, “he deliberately writes the story of his own and his government’s dishonour himself!”In the years after the Civil War, more and more politicians and generals agreed to publish autobiographies during their lifetimes.The most popular entry came from Ulysses S. Grant, who was driven to the project by his bankruptcy — and barely finished it because of a fatal cancer. Despite these challenges, Grant wrote a book that is generally seen as the greatest presidential memoir, although it focused on his time as a general.Personal Memoirs provided meticulous accounts of Grant’s battles. But the most memorable passages came in his descriptions of others — meeting with Abraham Lincoln, meeting with Robert E. Lee. That is the second quality Obama may consider: short, but memorable, character sketches of his contemporaries.The other thing about Personal Memoirs that should interest Obama is its anaemic impact on Grant’s legacy. When the book appeared in 1885, it sold more copies than just about any other title in American history. Before long, however, Grant’s military reputation began to falterPersonal Memoirs couldn’t reverse the image pushed by pro-Southern historians: that Grant was a blundering butcher.Yet, America’s presidents kept writing. When Theodore Roosevelt published his Autobiography in 1913, he inaugurated a streak in which, with the partial exceptions of William Howard Taft and George H.W. Bush, every president who has left the White House in good health has gone on to publish a memoir.These books have often repeated the problems present in Adams’s, obsessing over enemies and wallowing in self-justifications. Before he began writing, Roosevelt chatted with a novelist about his upcoming book.“I have no desire to get even with anybody,” Roosevelt said. Once he started writing, though, he couldn’t help it. The author compared himself to Lincoln; he compared his opponents to Buchanan.There is one surprising exception: The Autobiography of Calvin Coolidge, which appeared in 1929.While Coolidge’s book is forgotten today — as is Coolidge’s presidency, to be honest — it was a sensation in its own era. His contemporaries had always celebrated his writing. (The only thing H.L. Mencken liked about the 30th president, it seemed, was his literary style.) So the country’s biggest magazines entered a bidding war to publish the first excerpt from the eventual book, and Cosmopolitan, then a general-interest magazine, came out on top. On the morning the winning issue went on sale, Coolidge’s wife, Grace, went out early to buy a copy at her local newsstand. It was a good thing — by the end of the day the issue had essentially disappeared nationwide.Scalpers were selling it for several times the cover price; at the magazine’s headquarters, requests for additional inventory came from 1,900 cities.The passage that had everyone buzzing centred on Calvin Jr, the Coolidges’ teenage son. Early in his father’s presidency, Calvin Jr developed a small blister while playing on the White House lawn, a blister that became infected and ultimately killed him.Now, his father recounted the experience: ”In his suffering, he was asking me to make him well. I could not.” The most powerful person in America admitted that he had felt powerless — that, even years later, he remained lacerated and unsure. “If I had not been president,” Coolidge wrote, “he would not have raised a blister.” As he put it in the article’s final line, “It costs a great deal to be president.”Coolidge’s book rarely defended his presidency, but it presented a revealing portrait of his time in office. In fact, it contained a number of qualities Obama may want to borrow. It was modest. It was short. Most of all, it highlighted the human side of Coolidge’s presidency, capturing things only he could know.On some level, every past president has realised that this is the right approach. But they never follow through.When Dwight Eisenhower started working on his contribution, he promised a “personal memoir” — something that would skip the self-justifications to tell an intimate story. Then, Eisenhower wrote a two-volume tome that was as windy and indulgent as any of his predecessors’ books. When the first volume appeared, two weeks before the assassination of John F. Kennedy, it was widely discussed, including at the White House. Kennedy chuckled at Eisenhower’s self-righteous tone.“Apparently, he never did anything wrong,” the President told an aide. “When we come to writing the memoirs of this administration, we’ll do it differently.”Kennedy never got the chance, but his successor, Lyndon B. Johnson, also pledged a “personal” book. That has become the favoured description of one’s presidential memoir — Jimmy Carter and Bill Clinton used the word, as well — but it’s one of the emptiest promises in politics.Perhaps Obama is wrestling with these same authorial impulses. His previous works prove he is a terrific and personal writer, someone whose first book, Dreams From My Father, told a lyrical story while hinting at bigger themes.However, presidential memoirs present different challenges. Obama’s readers will, of course, want to know his thoughts on his administration and what has come after. But Obama can address those topics personally without bogging down in bland play-by-play.He doesn’t need to summarise every fight with Mitch McConnell, especially since Obama’s personality makes it seem unlikely that he would write about those squabbles in the gossipy way Adams wrote about Hamilton. Instead, Obama may explore what it felt like to campaign on a promise of unity, only to see that promise undone by broader political forces. He may describe what he thought and how he changed as he watched his deepest beliefs backfire.What Obama should do, in other words, is write a book like Coolidge’s. After all, attacking one’s opponents and vindicating one’s polices doesn’t really work.Even a memoir as good, and as popular, as Grant’s couldn’t secure him a favourable legacy. But that’s a cause less for despair than for relief — an excuse to write something shorter and rawer, something more intimate, something that really is “personal” — and that present-day readers will love to read. Don’t expound upon your theory of executive power — show what it felt like to be the executive. Reveal the presidency’s private side. Leave the rest to the historians. Craig Fehrman is the author of Author in Chief: The Untold Story of Our Presidents and the Books They Wrote