[Greg Mitchell writes the Media Fix blog for The Nation, where this piece first appeared. He is co-author with Robert Jay Lifton of"Hiroshima in American" and author of many other books.]

Sixty-five years ago today the Nuclear Age began with the first successful test of an atomic weapon at the Trinity site in the New Mexico desert. Earlier this week I wrote about the test and how it set the standard for much of what followed in the decades to come: radiation dangers, official secrecy and cover-ups, a nearly endless nuclear arms race, and the triumph of the national security state.

Now let's look at how it led to the actual use of the new weapon against Japan three weeks later.

One of the persistent -- and certainly the most influential -- arguments in the media for dropping the bomb over two highly-populated Japanese cities is that it saved hundred of thousands, even millions, of American lives that would have been lost in the"inevitable" U.S. invasion of Japan. Those numbers were grossly inflated from the start, many historians have shown, but any invasion would have been bloody enough. The significance of the Trinity success -- which was by no means a slam dunk beforehand -- was that it rendered virtually moot the plans for an invasion.

Why? There is no way any American president, and certainly not Harry Truman, would have gone ahead with an invasion -- scheduled for several long months after the Trinity test -- knowing that he had an A-bomb in his pocket. This helps account for why his surly mood at the Potsdam summit was transformed overnight by the news of the Trinity success.

The question, on the day after Trinity, was not, use bomb or invade (which defenders of the bomb still emphasize), but rather, how to use the bomb.

Truman's choices were: 1) inform Japan's leadership that the U.S. now had such a device (the Japanese knew what that meant, having tried and failed in its own atomic program), 2) set up a dramatic demonstration shot, 3) drop a bomb or bombs over a loosely-populated part of Japan or a military base, or 4) target large cities.

Those who continue to raise the specter of massive U.S. casualties (often citing a family member who might have perished) should be required to argue that options 1, 2 and 3 (above) would not have produced a Japanese surrender in the months leading up to the scheduled invasion and that Truman, when more A-bombs became available in the fall of 1945, would have then chosen to invade rather than drop the new weapons on the Japanese.

Again one has to say: No American president, and certainly not Truman, would have ordered thousands of Americans to their deaths rather than use more of the weapons. Consider, for example, our current use of drones in Afghanistan and Pakistan in place of large land forces.

The key issue surrounding all this, of course, is the prospect of ending the war through"negotiations." Now, many defenders of the bombing will say that the beauty of using the bomb against Japanese cities is this: It made the Japanese agree to unconditional surrender. This, of course, is nonsense. In fact, we accepted the very strong condition of letting them keep their emperor, which was always assumed to be the main sticking point in a surrender before Hiroshima.

In other words, we demanded unconditional surrender after Trinity -- but accepted a key condition after Hiroshima.

But would the Japanese have quit very shortly -- via the same"negotiations" -- if Truman had tried one of the first three options outlined above? Of course, we will never know for sure. Certainly there is evidence on all sides, and I'd need another 10,000 words here to even begin to discuss some of it (see my book with Robert Jay Lifton, Hiroshima in America).

One little known detail about Trinity is this: J. Robert Oppenheimer,"The Father of the Bomb," was so surprised by the incredible visual effects of the July 16, 1945, test that he came to believe that a demonstration shot might well have convinced the Japanese to quit (though he never urged this path, feeling the momentum to drop the bomb over cities was unstoppable).

What we also learned at Trinity: The radiation threat was even worse than we feared. That didn't stop Truman from speeding up the use of the bomb against cities.

The key historical fact usually ignored by defenders of the destruction of Hiroshima and Nagasaki is that the A-bomb wasn't the only reason the Japanese quit: The foe the Japanese most feared, the Russians, had finally declared war against them, and were on march, two days after the Hiroshima blast.

This was not a case of"getting in on the spoils" -- we had demanded that the Soviets do this at Potsdam the month before and knew it was coming, bomb or no bomb. This has led to theories -- which I have never fully embraced -- that the main reason we dropped the bombs, knowing Japan was already defeated, was to keep the Soviets out Japan, and intimidate them in the postwar era. I'd call this a reason, not the reason.

Be that as it may, there is no question that the Soviet declaration had a huge impact on the Japanese -- as it would have if we had merely demonstrated the A-bomb or dropped it over a more remote area in Japan. Truman, in his diary, declared that the Russian attack alone meant"fini" for"the Japs."

The key point is: We didn't wait around to find out if the Japanese would have surrendered to us shortly (especially after we let them keep the emperor) to prevent the Russians from invading, or if a strong nudge via use of our bomb would have been required.

So, for me (if not most others in the media), the onus has always been on the defenders of the use of the bomb to marshal evidence that all of those other options Truman could have tried after Trinity would not have produced a quick surrender.

Yes, we do know that surrender came shortly after Hiroshima and Nagasaki, but we also know the awful negatives of the decision Truman did make: the deaths of more than 200,000 civilians (mainly women and children) and lingering illness for thousands more, the staining of the U.S. with a moral stigma around the world (if not in our own country), plus the setting in motion of the sense of the weapon as desirable and usable, leading to a costly 40-year nuclear arms race.