Caitriona Palmer in Washington
Just a mile from my home in Washington DC, next to the banks of the wide and murky Potomac river, is a picturesque towpath, a tree-lined trail where I often stroll on weekend mornings with my husband and young children.
A couple of months ago while we were out walking, a fit-looking older man in jogging shorts and a T-shirt approached, shadowed in front and behind by two younger men. Noticing us, he slowed his impressive stride and sidestepped onto the grassy bank to allow us room to pass with our stroller.
"Do you know who that was?" my husband, a defence reporter said. "That was General Petraeus."
Weekend runs with his CIA guards along Washington's historic trails are now over for the soldier scholar after his life spectacularly imploded this week onto the front pages of the tabloids.
And one question is being asked by amazed observers: how could a man revered across America as the brightest CO of his generation, the shining intellectual star of the military, really be so stupid? Why did he temporarily lose his brain cells in the pursuit of a little extracurricular bedroom fun?
Such risk-taking is common with men of this calibre, says leading psychologist Frank Farley, who has conducted a study into why powerful men cheat. "The risk-taking personality has a bold quality. It's at the heart of great leadership, and sometimes it overrides what many Americans would call common sense," he said.
But the epic downfall of David Petraeus, the revered Princeton PhD soldier, the darling of policy pundits and politicians in Washington – and the man widely credited with rescuing the war in Iraq – has shocked even those used to Washington sex scandals.
A nation obsessed with celebrity and gossip has devoured the story of a nerdy-looking 60-year-old with a comb-over hairstyle and his vampish 40-year-old mistress. What, they ask, did she see in him? And why did he think he could keep their affair secret in, of all places, Langley, Virginia – headquarters of the CIA?
People who worked closely with Petraeus say that the four-star general was obsessed with his public image, jealously guarding his privacy and public access with a close cadre of brilliant young officers, many of whom had their own Ivy League doctorates.
These former staff officers are now asking how their boss, who preached about the importance of self-discipline and integrity and never betrayed a hint of stress or emotion while on active duty in Iraq and Afghanistan, could detonate a hand grenade in his own personal life with such devastating consequences.
By all accounts, Petraeus was a stickler for detail and asked a lot from those around him. A recently leaked CIA cable revealed how the top spy demanded that he receive fresh pineapple before bedtime while travelling, in addition to sliced banana over his breakfast cereal and a jogging route free of intersections or stop signs.
Military writer Tom Ricks, who recently wrote a book about Petraeus and other generals, said this week that the God-like atmosphere and mystique that surrounded the nation's top spook had a role to play in his eventual downfall. "I remember a friend of his saying: 'Dave Petraeus is incredibly good. He's better than the other generals you see here. The problem is he's not as good as he thinks.'"
Last month Petraeus and his wife of 38 years, Holly, were projecting an image of family love and unity as they celebrated the wedding of their daughter, Anne. This week, Holly was reported to be "beyond furious".
His wife – bespectacled, round faced and grey haired – could not be more different in appearance to Petraeus's mistress, toned and muscular Paula Broadwell, breathlessly described in the press as a wily temptress with "form-fitting clothes" and "expressive green eyes".
Petraeus married in 1974 shortly after graduating with top marks from the West Point Military Academy. At the time Holly's father, a four-star general, was superintendent of the academy.
But Mrs Petraeus – who moved her family 24 times in 37 years to follow her husband – has always brushed off suggestions that Petraeus married her to advance his career. "I'm not stupid. I wouldn't have married someone on the make. We got married because we fell in love."
That love will surely now be tested as Petraeus settles into a shockingly early and quiet retirement in the family home in a suburb of Virginia.
Perhaps there is comfort for Petraeus in the fact that his sex scandal is just the latest. Earlier this year, an army brigadier general, Jeffrey Sinclair, was removed from his post in Afghanistan after accusations of sexual misconduct.
Perhaps in Sinclair's case lies the answer to the question as to why America's most admired general would risk his career and family for a cloying, unpredictable woman 20 years his junior who he once referred to as his 'avatar'.
"I'm a general," Sinclair reportedly told prosecutors when asked about his demeaning comments towards women: "I'll do whatever the [expletive] I want."