[1] Many years after his death, his wife, Erica Gienapp, completed one of his final projects: The Civil War Diary of Gideon Welles, Lincoln's Secretary of the Navy: The Original Manuscript Edition (2014).
Gienapp's major scholarly contribution was his analysis of how the Republican Party suddenly appeared on the scene and quickly dominated Northern politics.
Gienapp argues that the great realignment of the 1850s began before the Whig party collapse, and was caused not by politicians but by voters at the local level.
The central forces were ethno-cultural, involving tensions between pietistic Protestants versus liturgical Catholics, Lutherans and Episcopalians regarding Catholicism, prohibition, and nativism.
Nativism was so powerful that the Republicans could not avoid it, but they did minimize it and turn voter wrath against the threat that slave owners would buy up the good farm lands wherever slavery was allowed.