Also, regional politics played an important role. Lincoln checked Douglas in his own region and handily carried the Northeast.
If Seward had been nominated, a Democrat could have picked up votes in the Old Northwest. With Southern votes such a Democrat could have won. Conversely, a New Yorker like Seymour just possibly could have beaten Lincoln.
I guess my point is here.
Grant, Hayes, Garfield, Arthur, Harrison, Cleveland, McKinley, Roosevelt, Taft.
9 presidents, from 1868 to 1912, everyone of them were from NY or Ohio.
Failed candidates:
Parker (New York), Seymour (Ohio), Greeley (New York), Tilden (New York),
Bryan (Illinois), Hancock (Pennsylvania), Blaine (Pennsylvania),