sigh
Look, you can drone on and on about the "Soviet Steam Roller" but the fact is that the primary advantage that the Soviets have is in numbers, and that has been shown to be only moderate rather than overwhelming. The western allies are pound for pound superior to the Soviets by a decent margin.
People make the assumption that the "soft" Western democracies will be at a major disadvantage compared to the draconian Soviets. Just because the Red army was able to order its troops on suicidal charges doesn't mean shit, the Japanese could do the same thing, look how good that turned out for them.
On the home front, it isn't nearly as baed as is made out, just like the Soviets aren't about to collapse into anarchy, the US/UK aren't about to suffer from civil insurrections. First off, if there is a war that breaks out in 1945, the provocation is enough to get two governments that have every reason not to fight such a war to do just that, public morale may be unhappy, but it won't suddenly result in riots in the streets. The democrats and Truman have until 1948 to worry about reelection.
As far as the situation "on the ground" let's look at how things would pan out. Let's assume that the Soviets are the aggressors and manage to pull off a surprise attack. The element of surprise and superior numbers will prove a decisive advantage in the first couple days at most. Allied forces will have to perform a fighting retreat across Western Germany. One assumes that this is a good thing, but immediately the logistical burden falls far more heavily on the Soviets.
The Soviet doctrine at the time relied heavily on a massive grinding slog while absorbing massive casualties and inflicting just as many on a numerically inferior opponent that is led by a maniacal Austrian who doesn't allow retreats. The Western allies will gladly oblige on the first part, not on the second, even Patton was smart enough to avoid getting suckered into a mass blood letting with a numerically superior enemy.
If the Russians decide to get into a long gun duel with the Western Allies, they will lose. In the air, the battle will be fierce, but the Soviets are at a considerable disadvantage. They lack decent early warning and radar systems, they have no integrated AA defenses, especially over Europe, and their aircraft are technically inferior to their allied counterparts, and they won't have the numerical advantage that the Red Army has. They also don't have a counter for, or experience fighting against massed flights of heavy multi-engine bombers with escorts.
Just to be generous(to the Russians), we'll effectively cancel out CAS by assuming that the Soviets have a really good showing in the air and manage to interdict enough Allied low flying combat aircraft to eliminate any Allied advantage in that department(at first anyway). This however does not account for Allied strategic bombers which will be carrying out round the clock sorties over every road, bridge, rail line, and supply depot in Soviet controlled eastern Germany.
An army is a hungry beast, an army on the offensive is ravenous. Even assuming that the Soviets keep a decent portion of their supply lines open even under heavy Allied bombing, we're still going to be looking at a massive shortage of fuel, supplies, and ammunition for the rampaging Red Army. The Soviets will either have to stop part of its advance in exchange for keeping up momentum in select areas, or bring the army to a complete halt until the supply situation is resolved. The second option is a nonstarter since time is not on their side and the supply situation will not be resolved quickly. The first option has the problem that it risks creating a salient which can be flanked and encircled, something which I'm sure the Allies will be looking for.
On the strategic front, Allied air forces will be launching sorties from just about every airfield within range into the Soviet Union, subjecting its already strained populace to an entirely new torment; that of strategic bombing. Expect round the clock sorties to every eil field in Soviet possession. Industrial areas previously untouchable by the Wermacht will now be getting pounded by the RAF and USAAF. Should the atomic genie be let out of the bottle, it won't be wasted on such foolish excercizes as trying to level entire cities, the US military will specifically target strategically important areas and targets. If major cities get hit, expect the militarily significant areas to be ground zero, not the city centers. So Moscow would be hit over the rail yards, and Kiev or Vladivostok over industrial areas. Even without massive structural damage to the cities themselves, the fires, radiation, and ensuing chaos from the nuclear detonations will render the targeted cities useless to the war effort for at the very least weeks if not months which should be just long enough for the US military to build more bombs and do the job all over again. I wonder how many times you have to nuke an industrial district before the Soviets will stop trying to rebuilt it?
When looking for a parallel to compare this conflict to, look to the Pacific war, not the Eastern front. Like the Japanese, the Russians will be facing an enemy which is man for man better than they are. Like the Japanese, they will have to rely on the Allies getting weary of conflict and suing for peace. Like the Japanese, the Russians do not have time on their side, they need to hit hard and fast and gain as much as possible and hope that they scared the Americans and British enough to get them to negotiate. Meanwhile, unlike the Germans, the Western allies are led by sane people, armies will be allowed to retreat. Unlike the Germans, the W Allies have better logistics. Unlike the Germans, the W Allies have rather modest goals(stop the Russians).
And please, stop with the whole "it's just 15 kilotons" or "it's only a million casualties" like those are small figures. Against an enemy bent on massacring practically every man woman and child in your country, that kind of thing can be endured, not against an enemy that is merely trying to stop you from conquering the western half of Europe.