Byrnes left the Supreme Court to head Roosevelt's Economic Stabilization Office, which dealt with the vitally important issues of prices and taxes. How powerful the new office would become depended entirely on Byrnes's political skills, and Washington insiders soon reported he was in full charge. In May 1943 he also became head of the Office of War Mobilization. Thanks to his political experience, his probing intellect, his close friendship with Roosevelt, and in no small part to his own personal charm, Byrnes was soon exerting influence over many facets of the war effort which were not technically under his departmental jurisdiction. Many in Congress and the press began referring to Byrnes as the "Assistant President."
He was a serious possibility for vice president in 1944. However, he was too conservative for the labor unions, big city bosses vetoed any ex-Catholic, and blacks were wary of his opposition to racial integration. The nomination went to Senator Harry S. Truman. Roosevelt brought Byrnes to the Yalta Conference in early 1945, where he seemed to favor Soviet plans. Writing in shorthand, his notes comprise one of the most complete records of the "Big Three" Yalta meetings.
I know in Alternate History Circles, we usually discuss if FDR had kept Wallace on the 44 tickect only to have him sworn in as the 33rd President in April of '45. But What If we looked at the other side of the coin and we asked What If Franklin had decided to the man he had developed a close friendship with, his assistant President James Byrnes as his Vice Presidential Running Mate in '44? I for one do not believe any particulary faction of the party would bolt, and they would probably begrudingly accept him as their VP Candidate. In the General Election, electorally I see FDR getting ridiculous numbers in the South but with Dewey outperforming in a few Northernstates but enough to give FDR his final landslide.
However what kind of President would Jimmy Byrnes be? He was definatley not a fan of Civil Rights, and there probably wont be any To Secure These Rights
program under his adminstration. But what about use of the atomic bomb, the Marshall plan, and relations with the Soviets? How does the '48 election turn out?