When President John F. Kennedy was assassinated in November 1963, American military deaths in Vietnam had just passed 50.
At the present loss rate, US military deaths in Iraq since the war "ended" two months ago will pass that total before the end of this month. Is this the start of an anti-American guerrilla war in Iraq?
Not yet, but it isn't looking good. In the early days many American soldiers' deaths were the result of vehicle accidents and the like, but recently most US casualties have been caused by Iraqi resistance fighters, and they aren't just sniping at isolated checkpoints.
They are ambushing US tank patrols with rocket-propelled grenades, making mortar attacks on American command posts - even shooting down an Apache attack helicopter.
American officials shy away from analogies between Iraq now and the Vietnam war almost 40 years ago, but it is getting hard to insist that the right analogy is with the post-1945 occupations of Germany and Japan.
For one thing, the pretext for sending US troops into Iraq - the fabled "weapons of mass destruction" - begins to look as flimsy and fabricated as President Lyndon Johnson's "Gulf of Tonkin incident" in 1964.
After two months of unhindered investigations and interrogations in post-Saddam Iraq, the only "evidence" for Iraqi weapons of mass destruction coalition forces have turned up are the trailers found in northern Iraq that were allegedly mobile germ warfare labs.
An official British Government investigation recently concluded, however, that the trailers really were mobile facilities for producing hydrogen gas to fill balloons that measure high-altitude winds, part of an artillery system originally sold to Iraq by the British company Marconi Command and Control - just as the Iraqis claimed.
So is Iraq the new Vietnam? Maybe, but one big difference is that so far US casualties are concentrated in the so-called Sunni triangle extending north and west from Baghdad, where Saddam Hussein's ruling Baath Party had the deepest roots. Sunni Arabs account for only about 20 per cent of Iraq's population - about 5 million people.
American deaths in this region have been running at five a week recently. Run that average forward for 16 months, and President George W. Bush would have a further 350 American combat deaths to account for when the US presidential election comes around next year.
That would be awkward, but he might get away with it if he could persuade Americans it was all part of the "war on terrorism". The bad news for Bush is that the fighting may well escalate in the Sunni triangle - and the Shia majority may start resisting the occupation, too.
During the next three months Iraq is too hot even for the Iraqis, but in much of the US-occupied zone there are no reliable supplies of water - or other public services.
The US viceroy, Paul Bremer, disbanded the entire Iraqi Army last month with one month's severance pay, ensuring that many tens of thousands of experienced officers and NCOs will have nothing to do this northern summer but nurse their resentment.
As of last Saturday, the two-week gun amnesty ended and every Iraqi possessing a gun without a permit can be arrested. But all rural Iraqis own guns, and by now, thanks to the rampant insecurity, so do three-quarters of urban Iraqi households.
Add to the mix an occupation force that is still starved of troops by Pentagon policy, and nervous American soldiers who use enormous firepower whenever they feel threatened, and it may be a very long, hot summer.
By the end of it, Sunni Arabs and US troops could be in the sort of escalating confrontation that has no exit - and it is a delusion to imagine that the Shia majority are America's allies.
They are waiting to see if they can win political power without fighting the US, but if they conclude that the Pentagon is determined to impose its pet Iraqi exiles on the country then they will fight, too.
Iraq is not bound to become America's second Vietnam, but it is drifting rapidly that way.
This was always possible, given the vast gulf between Washington's declared motives for the invasion and what most Iraqis think America's real motives are, but it has been made more likely by the monumental incompetence of the post-conquest administration of Iraq.
The Shia are still holding their fire, but it's hardly surprising that the Baathists are re-surfacing in the Sunni Arab parts of the country.
Which explains what's happening now in the Baghdad suburb of Mansour, where American missiles struck a restaurant where US intelligence thought Saddam was eating on the next-to-last night of the war.
From that night until last week, long after the neighbourhood's families had retrieved the bodies of their dead, the site was not visited or guarded by US troops. Is Saddam dead? Who cares?
But now the site is sealed off and American forensic investigators are digging frantically in the rubble, hoping to find evidence that Saddam is really dead.
As though that would change anything.
Herald Feature: Iraq
Iraq links and resources
<I>Gwynne Dyer:</I> US faces long, hot summer in deadly tinderbox
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