I think you're on the right track here. Wallace was still a pronounced anti-Communist as late as 1946. It wasn't until Truman fired him that Wallace cozied up to the far left, certainly out of resentment towards Truman. (And also because, as
@David T has pointed out in earlier threads, Wallace was shunned by the majority of liberals to the point where he depended on the far left for political support). After the 1948 election, Wallace returned to his anti-Communist views and supported the Korean War. He even supported Nixon over Kennedy in 1960, although he warmed up to JFK after his inauguration.
That said, I'm concerned about his apparent desire to share atomic secrets with the Soviets. He would run into a great deal of opposition from the military on that one. Given Wallace's inconsistent political views throughout his career and weak leadership as VP under FDR, there's a chance that someone like George Marshall would be able to talk Wallace out of it. Or the military would simply refuse, and Wallace would back down to avoid antagonizing the high brass. By 1948 however, Wallace would be just as convinced of the Soviet threat as Truman and I imagine that the Berlin Airlift and a sort of "Wallace Doctrine" would occur. Even if Wallace is more interesting in using diplomacy to counter the Soviets than Truman was.
Erm Marshal was FOR inviting Soviet scientists to the Trinity Test.
Likely the US won't unilaterally decide to rewrite the Yalta agreements and then accuse the Soviets of breaking them. NO abrupt end to lend lease then resumption. He probably continues FDRs policies rather than the complete 180 that Truman did.
I would minimize the general Soviet problem as much as possible because these problems, in one form or another, seem to arise every day and most of them straighten out as in the case of the Bern meeting.
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We must be firm, however, and our course thus far is correct.
April 11, 1945.
Wallace would listen to his military advisors and NOT use the atom bomb on Japan.
"the use of this barbarous weapon at Hiroshima and Nagasaki was of no material assistance in our war against Japan. The Japanese were already defeated and ready to surrender... in being the first to use it, we had adopted an ethical standard common to the barbarians of the Dark Ages. I was not taught to make war in that fashion, and wars cannot be won by destroying women and children." - Admiral Leahy
"I told him I was against it on two counts. First, the Japanese were ready to surrender and it wasn't necessary to hit them with that awful thing. Second, I hated to see our country be the first to use such a weapon." - General Eisenhower
"the first atomic bomb was an unnecessary experiment... put out a lot of peace feelers through Russia long before" - Admiral Halsey
"If at any time the USSR should enter the war, all Japanese will realize that absolute defeat is inevitable." - April 11 Joint Intelligence Staff Prediction
Hell he'd even read the telegrams from Japan practically begging for peace.
"telegram from the Jap emperor asking for peace." - excerpt from Truman's diary concerning July 18 intercepted cable
S he could either modify the surrender demand as MacArthur suggested and tell them they could keep the Emperor and they surrender in MAY as MacArthur maintained till his deathbed. Or Wallace simply waits for the USSR to enter the War and the Japanese surrender for the same reason in our world.
"the Soviet Union will take not only Manchuria, Korea, Karafuto, but also Hokkaido. This would destroy the foundation of Japan. We must end the war when we can deal with the United States." - Prime Minister Suzuki
“There was little mention in the Japanese cabinet of the use of the atomic bomb by the U.S. The dropping of the bomb was the pretext seized upon … as a reason for ending the war. But … it [is] almost a certainty that the Japanese would have capitulated upon the entry of Russia into the war.” US War Department report in 1946.
The without the racist f*****r Jimmy Byrnes at the London conference literally threatening Molotov, again after Truman shouted at him during their first meeting, you likely get a better result, especially if the US keeps to Yalta unlike OTL.
“You don’t know southerners. We carry our artillery in our pocket. If you don’t cut out all this stalling …, I’m going to pull an atomic bomb out of my hip pocket and let you have it.” - Jimmy Byrnes
Without the US provocations you avoid Germanies division, and you likely avoid the arms race as per Anatoly Gromyko.
“set the heads of the Soviet military spinning. The mood in the Kremlin, in the General Staff was neurotic, the mistrust towards the Allies grew quickly. Opinions floated around to preserve a large land army, to establish controls over extended territories to lessen potential losses from atomic bombings.” - Anatoly Gromyoko
Hell the bombings even changes Eisenhower's views.
"before the atomic bomb was used, I would have said, yes, I was sure we could keep the peace with Russia. Now I don't know... People are frightened and disturbed all over. Everyone feels insecure again." - Eisenhower
If Wallace follows J Davies advice.
“I have found that when approached with generosity and friendliness, the Soviets respond with even greater generosity... The ‘tough’ approach induces a quick and sharp rejoinder that ‘out toughs’ anyone they consider hostile.” - Joseph E Davies former Ambassador to the USSR
Maybe he follows Stimson's lead and we get some kind of international control of the atomic weapons technology without the senseless bombing of Japan feeding Soviet fears.
if we … hav[e] this weapon rather ostentatiously on our hip, their suspicions and their distrust of our purposes and motives will increase.… The chief lesson that I have learned in a long life is that the only way you can make a man trustworthy is to trust him; and the surest way to make him untrustworthy is to distrust him and show your distrust." - Henry Stimson Secretary of War
So in conclusion you likely avoid the Cold War, the Soviets will be less likely to impose regimes in Eastern Europe and will likely remain as Hungary was, free elections with some Soviet influence over policies, a mutually satisfactory arrangement over Germany, likely neutralised with no military, with a possible continuing set of say inspections by allied forces. With luck a more successful Operation Safe Haven, the BIS gets shut down and those Nazi Collaborators like Allen Dulles, John Foster Dulles actually face their crimes, with leads to a far less dangerous and outright evil CIA. Maybe a greater awareness of said Nazi collaboration and less 'Greatest Generation crap'. He'd probably work more through the UN like UNRA rather than a unilateral plan like the Marshall OTL plan.
No US provocations in Germany means no Berlin blockade.
Hopefully Wallace unlike Truman doesn't hand Greece back to the Nazis as the British convinced him to do, maybe he tells the French to f**k out of Vietnam in return for aid so Ho gets his desired US backed independent state.
Would Wallace win in 1948, maybe, he'd certainly beat Dewey who was close to the Dulles brothers who'd actually be known as Nazi collaborators and traitors in this timeline, as would many others in the business and Wall Street elite, certainly Forestall won't get the chance to buddy up with Nazi terrorist groups like Nightingale, Gehlen gets to face his comeuppance at Nuremberg. Karl Wolf a SS high up who served as go between between Hitler and Himmler and was rescued by Allen Dulles faces his crimes and gets sent to Nuremberg.
No exaggerated and entirely nonexistent Soviet threat and no US started Cold War