I am glad that Lott is no longer the majority leader. But as usual the Republicans did the wrong thing at the wrong time for the wrong reasons.
No, but he could have cost Truman the election. Punishing Truman by denying him the White House would have sent a message about integration to both major parties.
No Republican could have carried Alabama, Mississippi, Louisiana, or South Carolina in 1948. Memories of the Civil War, Reconstruction, the Depression and the New Deal ran deep.
But that a Democratic President who had been quite unpopular won without those Deep South states was truly unexpected. Truman held the Upper South. The West and most of the Middle West came through for him as well, as did Texas and California. Dewey carried the Plains States and such New Deal big labor states as Michigan, New York (his two home states), and Pennsylvania, as well as other Eastern states.
1948 was very different from later elections, when Republicans dominated the South and West, and Democrats had their strength in the Northeast. Maybe Carter in 1976 was the closest parallel.