The 1860 election, like political debate since at least 1854, had been dominated by the issue of the expansion and preservation of slavery. Di Lorenzo has picked letters containing the few or the only references to the tariff in Lincoln's writings and utterances of the campaign and used his obsessions to build a case that everything was all about the tariff.
Lincoln did not need the tariff to get elected. If he could carry Indiana, he was likely to carry Pennsylvania, particularly with Pennsylvania favorite son Buchanan out of the race. Who else would iron-makers and other Pennsylvanians vote for anyway?
Henry C. Carey was more than a lobbyist or propagandist. He was a respected economist of his day. Pro-tariff theorists and businessmen seeking tariffs would naturally flex their muscles and make a display of how essential they were to Lincoln's victory. This sort of behavior is known to us even today. But such claims should not be taken at face value.
There is something bizarre about Di Lorenzo's argument. On the one hand we are told that Lincoln was a high tariff man going back for years. On the other hand we're told the tariff was something promoted to win the election. Di Lorenzo should realize that he can't have things both ways: either the tariff was a long-standing part of Lincoln's world view, as it was of American politics, or else it was adopted on cynical and purely political grounds.
On the one hand we are told that the South was justified in going to war to promote its cotton-growing (and slaveholding?) interests. On the other it's said that iron masters were wrong to vote for their own interests and politicians were wrong to appeal to the interests of American manufacturers.
Those two aren't mutually exclusive, and I didn't gather that they were from DiLorenzo's article. Lincoln was a high-tariff man and the tariff issue in the 1860 election was calculated to play well in the more populous north.