At that time, we had zero, zilch, nada atomic bombs.
The first successful *test* of an atomic bomb was on July 16, 1945, three months after Roosevelt died.
I am not a fan of Roosevelt, but to claim he should have acted differently with Stalin at Yalta, because we had overwhelming atomic superiority, when we had not even successfully tested an atomic bomb, is rather a stretch.
Truman considered "dropping a bomb" on Stalin, quite a bit later.
Would the U.S. population have stood for it?
Highly unlikely.
The full perfidy of Stalin and the Soviets was not understood until well after WWII was over.
Looking from the view of the Russians/Soviets, where they had just lost 12 million people in a war with the Germans, for the second time in 30 years...Their takeover of eastern Europe as a buffer zone is more understandable.
Everyone in the West was tired of war. No one was willing to start another war to fight for Poland, the Balkans, the Czechs, Hungary, Lithuanian, Estonia, Latvia. Some of these had fought with the Germans.
It was not the easy, go/no go decision you describe.
Ever heard of Yalta? Operation Keelhaul?