Had he not tricked the nomination away from Seward, a President Seward likely wouldn't have triggered either a secession or a civil war.
Lincoln was like an intelligent Bernie Sanders of his day; Too far out liberal to win acceptance by people who saw him as a potential threat to their status quo. Seward would have likely been tolerable by the South, especially if he expressed interest in their concerns and tamped down the rhetoric that they were evil people.
McClellan should have won the election of 1864.