Roosevelt - dead man (not) walking at that point. Two months to go. At least he had the decency to replace an overt communist with a democrat party hack as VP before he died.
There was nothing decent about that man. He was most likely forced to dump Wallace.
And the Communist ran against the hack (as a “Progressive”) in the subsequent election.
Actually Roosevelt had next to nothing with the decision to run Truman as VP in place of Wallace. In those days, the party big wigs selected the VP candidate, not the President.
They wanted Wallace out, Truman seemed to be the best bet to replace him. Truman told them what they could do with the VP nomination in no uncertain terms. On the last day of the Democratic Convention, they got Truman into the proverbial smoked filled room and laid out the facts of life to him. The told him that who ever was the VP would be the President within a year. They knew what Roosevelt’s health condition really was (as big a secret as Overlord or Manhattan Project). They told Truman, if he didn’t accept the VP nomination it would go to Wallace. Truman hated Wallace and said that he would accept the VP nomination.
At least before he end of his life, Wallace, realized the error of his ways, and became a strident anti-communist, he was just very naïve at that time.