We know that General David Petraeus, the former head of the CIA, had an extramarital affair. He has admitted it, though he denies his relationship compromised America’s national security.

But I am beginning to wonder whether the Pentagon’s investigation of General John Allen, the US commander in Afghanistan, for “inappropriate” emails allegedly sent to a woman in Florida has left a fine soldier unfairly besmirched.
General.BLOG  General John Allen: a fine soldier unfairly besmirched?
Allen succeeded Petraeus in Afghanistan, though the two men are so different that those who know them say they hate each other.

Petraeus’s infidelity with his biographer may have stemmed from a degree of narcissism which earned him the nickname “King David” in Kabul.

He was well known for not missing an opportunity to point out that he devised America’s counter-insurgency doctrine which resulted in the “surge” of troops in both Iraq and Afghanistan.

The most famous general of his day would schedule one-hour sessions every week, when troops could be photographed alongside him.

In his relationship with his biographer, the Petraeus personality cult apparently got so out of control that it finally enrolled Petraeus himself.

John Allen is a very different character. Inclusive, diplomatic, a team player loved by his troops.

“If he did wrong, he would admit it and resign, no question,” a friend of Allen’s told me, describing as “stupefying” Allen’s capacity for hard work.

Soldiers testify that it would be ridiculous if Allen’s appointment as supreme allied commander at Nato should now be cancelled, because he would be so very good at the job.

America’s defence secretary, Leon Panetta, is standing by his man as well. “He certainly has my continued confidence,” Mr Panetta said of Allen this week.

The general remains in command of 68,000 American troops and has denied any wrongdoing. I suspect that the Pentagon’s inspector general is investigating Allen because, in the wake of the Petraeus affair, no stone is being left unturned.

I am told that Allen often deals with 200 to 300 messages in his inbox every day, and factors in time to deal with them all.

A large batch were apparently from an attractive 37-year-old socialite he had met in Tampa, Florida, but whether they crossed the line from affectionately familiar to flirtatious, we cannot know because we haven’t seen them.

Not that flirtatious need matter much, anyway. Adultery may lie outside the American military code of behaviour, but friendship certainly does not.

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