I received a message from the mods on this question (I'm not, to my knowledge, a flaired user, but no matter).

Part 1 (Apparently there's a 10000 max...and I managed to go over), so Part 2 will be a reply to this).

It is indeed a great question! There are several contentious parts to this question (I think that's a good thing), and I'll just flag one before proceeding - this is a bit of a historical-philosophical debate, but if it can't be raised in this subreddit...I'm going to raise it, and then address one part of your actual question. (Also note I'm going to use atomic and nuclear basically interchangeably, but of course the U.S. didn't have a deliverable thermonuclear device until March, 1954...but the difference between megaton and kiloton, or that Stalin, Khrushchev, Truman, Eisenhower, et al. would have treated an atomic vs. a nuclear attack on their respective territories, are for my purposes negligible).

When did the Cold War begin? Your question suggests the Cold War had not fully begun until some nondescript date after the end of the Second World War. That's a completely reasonable assertion, and there are plenty of reasons one can look to the post-war period between the end of the war and some time before the beginning of the Korean War as a not-truly Cold War period.

It is of course not a novel debate that centres around the origins of the Cold War. Geoffrey Warner wrote a good article on the "field" up to that point way back in 1990 (Diplomacy and Statecraft, Issue 3), and even there he noted the debate had been ongoing for decades, with some putting forward arguments that the origins should be traced at least back to the late 19th century when America and Russia began to openly vie for influence wherever England's grip loosened.

Based on my own research, experience, reading, I see the Cold War, as we tend to think about it, having its clearest origins in late 1942. In this period, both the U.S.S.R. and the United States were attacked, for the second time in less than thirty years, by powers holding views/ambitions/systems anathematic to their own. Both states already held views that the "old world" was insufficient, rotten, or in other ways ill-conducive to their system's potential peaks, but had to that point been seemingly content to chip away and erode those systems gradually. Being challenged, threatened, and otherwise damaged by both the ambitions of regional competitors and their own failure to anticipate and prevent such ambitions (along with the shared belief that the previous attempt of the Old World to settle and hold back such things with the Versailles Treaty had to be the final attempt the Old World was given for such things), set both juggernauts on a path in which the only way they could feel safe in the world system was to reshape it from a position of strength along the proper (read; their) path.

To simplify so that I can get to your central question, it was at this point, that even if not everyone in power in the U.S. and U.S.S.R. acknowledged it (which is never the case anyway), their two systems were going to come into direct conflict by dint of the fact that both were, in 1942, determined to instil and assert the solution to problem from which they and the world suffered - the Cold War was the result of the fact that two superpowers disagreed on the correct solution.

At last I labour toward touching on your actual question! Unsurprisingly, I'll give some thoughts/perspectives on Eisenhower. I want to acknowledge that pinpointing a precise date for a topic like this is problematic - not the previous rambling about "when did the Cold War begin?" but more along the lines of, when did Dwight Eisenhower's conceptual framework for nuclear weapons solidify into the state it was in by the time he became President? Because, ultimately, we know most about what Eisenhower thought about nuclear weapons during the time he was President.

The argument I'll put forward is that his understanding and perspectives remained fairly consistent from the war period into the interwar period, and into the Cold War. I'm going to acknowledge that in giving this answer, I'm very much open to the criticisms that, given Eisenhower's management of his historical image, his, as Nixon put it in his own memoirs, "complex and devious" nature, and the fact that this is still very much an ongoing debate, I'm providing a simplified or abridged portrait.

My Answer:

The short version: Eisenhower either believed atomic and nuclear weapons were an order of destruction so incomprehensible that the should never be used because if they were used they'd be used like every other weapon we've ever had, or Eisenhower believed the first part but thought there might be some specific scenarios in which such weapons could be used.

The long but still not complete answer:

Eisenhower believed that nuclear weapons would be used in future conflicts, he famously (in 1954, during a crisis - so keep that in mind) stated that if the United States became involved in a conflict it would treat nuclear weapons the same as any other weapon, and would use them tactically, but would consider them and utilize them "exactly as you would a bullet."

One could, and SHOULD point out that Eisenhower rather famously voiced moral objections to the bombings of Hiroshima and Nagasaki during and shortly after the Second World War. One should also point out, as Brian Madison Jones did in his dissertation, that Eisenhower made these objections known later, and in public...and when it became "politically convenient" in 1948 - historians have struggled to find evidence he actively or forcefully objected to the bombings at the time.

This is important, because Eisenhower wrote in his diary in 1950 and into 1951, multiple times, that the United States should use atomic weapons to break the stalemate in Korea (including dropping atomic bombs on China). Eisenhower even wrote up and devised a plan that included the use of atomic weapons and sent it to the DoD and White House. So in this post-war period we have at best a mixed message (Eisenhower historians eat mixed messages for breakfast).

But does this mean Eisenhower's mind changed, or remained consistent? Campbell Craig (Destroying the Village, 1998), and others, like Brands, argued that Eisenhower as President had been so shaped by his time as a general and in the pre-Cold War period that this "exactly the same as a bullet" quote was both true and untrue at the same time. What this means to historians like Craig is that Eisenhower, educated in Clausewitz at West Point, considered it ridiculous to presume that any power would hold back using a weapon in a life-or-death struggle. Here, I agree with Craig.

Where I differ is that Craig concluded that Eisenhower, who certainly did grasp the annihilatory capacity of such weapons, therefore decided to present their use as always an all-or-nothing proposal - with Craig believing this suggested Eisenhower secretly refused to use them at all. To summarise this vein of historical thinking: Eisenhower believed that if the U.S. used nuclear weapons in a conflict, be it with North Korea, China, the U.S.S.R. or otherwise, it would result in total nuclear obliteration since it would inherently embolden, or perhaps require (if the conflict was with the U.S.S.R.) other nuclear powers to use their weapons in their own conflicts. From that belief, the conclusion Eisenhower came to was that he had to make every attempt to prevent any use of nuclear weapons.

My perspective (and that of historians like Martha Smith-Norris) is that Eisenhower never fully abandoned the idea that one might use nuclear or atomic weapons in a tactical, non-ultimate fashion.