Too pro-Democratic, I think. A Republican Party that can play as sort of a 'White Working Man's' party in the South will make OTL border slave states potential swing states too. On the whole, I see the GOP as stronger than the Whigs, partly because of demographic and economic change, though i think the Democratic Party still has some advantage if it can avoid crazy factionalism. Remember that OTL Southern democrat leaders pushed the factionalism because even though it hurt the party as a whole, it increased their power personally.
Too Democratic in what way?
They only need to do a couple of percentage points better than OTL - and TTL they are not under a cloud for suspected wartime disloyalty, nor is there any "Grand Army of the Republic" to rally votes against them - and of course there's no black vote even in most of the north.
In 1868 the popular General Grant, running while the war was still fresh in everybody's mind, carried CT and IN by less than three percentage points, and couldn't carry NY or NJ at all. In 1880 and 1888 Garfield and Harrison carried NY and IN by less than two percent. That's all the shift the Democrats need.
As for forming an antislavery party in the South - well, as David T has already noted, states like KY and DE were turning down Lincoln's gradual emancipation proposals even when slavery was clearly doomed, and clinging on to the institution until the bitter end in Dec 1865. And look at the lopsided majorities by which KY rejected Lincoln in 1864 and Grant in 1868. And (given the rarity of two-term presidencies in this era) Lincoln almost certainly has only four years in which to do it - four years in which the Democrats control both houses of Congress, and his patronage consists of little more than a few Postmasters and the like. And even these have to be confirmed by a Democratic Senate. Sure he was a capable politician, but how much can he really do under such conditions?
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