I consider myself completely qualified to review these diaries because, for a long time, I would not have believed that Ronald Reagan could have read them, let alone written them. During the 1980s in Washington, I was part of a school of journalism that mocked the president for owning more horses than books. I made a particular point of lampooning his easy, deceptive style; his sinister musings on Armageddon as well as his naive nostalgia for a forgotten Norman Rockwell ideal of middle America. In harsher mode, I attacked his Manichean anti-communism, his affectation of “faith” and his softness on right-wing dictatorships. And I was always maddened at the way that his charm and his apparent near-senility would get him through difficult moments at press conferences.

I don’t take all of this back, by any means. It still enrages me to remember the way he stuck up for the South African government, for example. And I can recall being quite frightened at the two times the United States came nearest to a military coup, first when General Alexander Haig seized the microphone on the day that Reagan was shot, and second when it was revealed that a dodgy marine colonel named Oliver North had been running a private ultra-rightist foreign policy from the basement of Reagan’s White House.

And now I pick up these amusing and enlightening diaries, as edited by the historian Douglas Brinkley (who was a close friend of the late Hunter S Thompson yet who dedicates the book to Nancy Reagan), and I have to resort to the reviewer’s cliché and say that I quite simply couldn’t put them down. Here’s an entry from March 24, 1981, describing a paranoid telephone call from General Haig, who was then secretary of state: “Al thinks his turf is being invaded . . . He talked of resigning. Frankly, I think he’s seeing things that aren’t there. He’s Sec of St and no one is intruding on his turf – foreign policy is his but he has half the Cabinet teed off.”

That’s a few days before Reagan survived John Hinckley’s fusillade of bullets, after which Haig appeared sweating and megalomaniac on prime time. Then on June 25, 1982: “Today was the day – I told Al H I had decided to accept his resignation. He didn’t seem surprised . . . Up to Camp David where we were in time to see Al read his letter of resignation on TV. I’m told it was his 4th rewrite. Apparently his 1st was pretty strong – then he thought better of it.”

So which is the real Ronald Reagan: the one who gave the secretaryship of state to a rather, er, volatile man, or the one who saw that he had a problem with him? It’s Reagan’s serenity in the face of such questions that makes one whistle. Sometimes his intuition about foreign statesmen is oddly sharp (“Sharon is the bad guy who seemingly looks forward to a war”) and sometimes it’s amazingly dumb (“Pres Zia of Pakistan is a good man (cavalry). Gave me his word they were not building an atomic or nuclear bomb”). And then there’s the way that he signs off the day: “State dinner a huge success – a really fun time and great entertainment by Perry Como and Frank Sinatra [March 25, 1982].” “Nancy came home about 6pm – thank Heaven. We watched tapes of Princess Grace’s funeral [September 18, 1982].” “Only dark spot of day was a real one – a notice that Fred Astaire had died. He was a truly wonderful man [June 22, 1987].”

It seemed at the time that Reagan wasn’t even a showbiz figure, but rather a man fixated on the second-rate elements of Hollywood. Yet this celeb-struck person could record a shrewd observation before turning in. I give you this hilarious entry from May Day 1981: “Highlight was noon visit by Prince Charles . . . The ushers brought him tea – horror of horrors they served it our way with a teabag in the cup. It finally dawned on me that he was just holding the cup & then finally put it down on the table . . . Mike [Deaver] escorted him back to the White House and apologised. The Prince, ‘I didn’t know what to do with it.’ ” In two separate entries on the Middle East, one of them just after he receives news of the Israeli bombing of Saddam Hussein’s nuclear reactor, Reagan goes even further than I used to fear, and broods on the end of days, concluding by saying: “I swear I believe Armageddon is near.” Yet this idiocy has the paradoxical effect of making him extremely serious about arms-control discussions with the Soviet Union. In December 1985 – really quite early – he minutes his hope that a missile shield “could render nuclear weapons obsolete & thus we would rid the world of that menace”. All the subsequent entries have the effect of demonstrating that he saw the point of Gorbachev, and of glasnost and perestroika as if by some untutored instinct. That’s a better track record than was demonstrated by many more liberal cold-war “experts”.

And this, in a way, is the point of studying the Reagan years in retrospect. There were all sorts of unspoken political borders, policed by pollsters and academics, that it was considered unsafe to cross until Reagan breezily crossed them. He was wrong on an amazing number of things, and he makes some astonishing admissions of incompetence and inattention – especially regarding the Iran-Contra imbroglio that could have led to his impeachment. He is almost alarmingly candid, for a “family values” politician, about the distraught relations between himself and his estranged children. Yet he was convinced that new-deal economics were subject to diminishing returns, and certain that the Soviet Union was moribund.

And an average voter or reader can see his mind working and watch him getting bad tidings and think: yes, this is how I might have faced the situation if I were the president. The knack of phrasing things like this is what some call populism, but it is a trick that few self-declared men of the people actually succeed in bringing off. My favourite entry is the laconic and penultimate one, from January 19, 1989. “Tomorrow I stop being President.”

A day in the life

Monday, March 30, 1981: “Left the hotel at the usual side entrance and headed for the car [pictured above] – suddenly there was a burst of gunfire from the left. Secret Service agent pushed me onto the floor of the car & jumped on my back. I felt a blow in my upper back that was unbelievably painful. I was sure he’d broken my rib . . . .

By the time we arrived [at hospital] I was having great difficulty getting enough air. I walked into the emergency room and was hoisted onto a cart where I was stripped of my clothes. It was then we learned I’d been shot and had a bullet in my lung.

Getting shot hurts.”

The Reagan Diaries edited by Douglas Brinkley

HarperCollins £30 pp783

Available at the Books First price of £27 (including p&p) on 0870 165 8585

Read on... books:

President Reagan: The Triumph of Imagination by Richard Reeves (Simon & Schuster £20). Account of Reagan in the White House.

Times Recommends

• The 100 Best Books of the Decade
• The Times picks the 50 best paperbacks of 2009
• The conversation: James Ellroy