Although the POD needs to be totally redone, BUT, i REALLY want to see where you are going with this.
Why would Lincoln dying affect anyone's vote? If Lincoln died, then Hamblin would take office. It wouldn't make any difference either way to most voters.
14. That the Republican Party is opposed to any change in our naturalization laws, or any state legislation by which the rights of citizenship hitherto accorded by emigrants from foreign lands shall be abridged or impaired; and in favor of giving a full and efficient protection to the rights of all classes of citizens, whether native or naturalized, both at home and abroad.
I think the POD would be because of the Republican platform. Like has been noted above he didn't campaign. But his adherents did. And at the time the Republicans were a wild coalition. They had suffragists, know-nothings and all kinds of other zanies in there.
Two big poisonous issues for Lincoln. Anti Immigration and very high tariffs for public works. If his adherents push issues like suffrage, anti immigration and high taxes Lincoln would loose lots of support. He would forgo MA and NY on both those issues. sufferage might cost support in other marginal areas. On the Immigration issue he would defintily loose CA and OR in addition to MA and NY.
Taxes are never popular at election time. Between elections there are always folks who want to spend more money, but at election time, there are not. These things could easily cost Lincoln four or five states which we could give to Breckinridge.