The US forces obviously were not the only counter forces in Europe. It wasn't just ~300,000 US troops vs the entire Red Army.
It was: the US, the UK, France, Western Germany, Italy, Netherlands, Denmark, Belgium, Portugal, Greece, Turkey. Russia also very likely would have lost several of its western post WW2 Soviet Union territories in the chaos.
The US could bomb Russia from all over Europe. Russia couldn't sustain a meaningful bombing campaign against the US mainland. Russia also had a mediocre navy compared to the US. Rapid attrition would have guaranteed a Russian loss.
Russia was very weak for 30 years after WW2 (really their entire existence except for the brief oil boom of 1974-84). While the US was in the exact opposite position. Timely US reinforcement probably would not have been necessary. That's a war that would have gone on either for years, or for a few weeks. Russia also would have had few allies in a European war. The US had the manpower, financial and manufacturing ability to stay in a long-term fight with Russia, whereas Russia could not have afforded to stay in it. They could have never replaced their war manufacturing after the US destroyed it with aerial bombing, and the war would have ended there (in the non-nuclear scenario). Russia would pull out the nuclear card, an equivalent of suing for peace, and that would have been that.
It was: the US, the UK, France, Western Germany, Italy, Netherlands, Denmark, Belgium, Portugal, Greece, Turkey. Russia also very likely would have lost several of its western post WW2 Soviet Union territories in the chaos.
The US could bomb Russia from all over Europe. Russia couldn't sustain a meaningful bombing campaign against the US mainland. Russia also had a mediocre navy compared to the US. Rapid attrition would have guaranteed a Russian loss.
Russia was very weak for 30 years after WW2 (really their entire existence except for the brief oil boom of 1974-84). While the US was in the exact opposite position. Timely US reinforcement probably would not have been necessary. That's a war that would have gone on either for years, or for a few weeks. Russia also would have had few allies in a European war. The US had the manpower, financial and manufacturing ability to stay in a long-term fight with Russia, whereas Russia could not have afforded to stay in it. They could have never replaced their war manufacturing after the US destroyed it with aerial bombing, and the war would have ended there (in the non-nuclear scenario). Russia would pull out the nuclear card, an equivalent of suing for peace, and that would have been that.