It would have been useful to know if the story actually appeared in the Sun (or the Exchange for that matter. There actually is an image of a page of the Exchange online that is supposed to have the story. But you say you can't release an image from the Sun. That's nice, but it doesn't resolve the question.
You also say that there are various accounts of Lincoln saying the "What about my tariff" line. Of course there are. It became part of the folklore (if it wasn't folklore all along). It was repeated time and time again in different versions and contexts. But we still don't know if Lincoln actually ever said it. We can be pretty sure that a lot of those variant versions weren't said by Lincoln.
Moreover the context is lost. If Lincoln said it, was it really a jaw-dropping moment that revealed his inner-most motivations, or was it one of many things said in the conversation? Plenty of the versions that have come down to us have clearly been "remembered" so as to make the tariff more central than it may have been.
Indeed, just this week we've seen yet another prime example of the press's unlimited ability to strip words from their full context to make the speaker look, well, stupid.
Of course, I'm referring to the 40 minute press conference Trump gave in Scotland, on the occasion of the Brexit vote.
In the midst of a long discussion of possible effects, Trump mentioned a weaker British pound would mean more tourist visits, good for his Scottish golf course.
Well, the press went nuts!
Stripping away the context, as if he'd said nothing else, the despicable media made it look like Trump only cares about golf, while the European Union is crashing down around him.
So context is everything, and Lincoln's comment here is certainly appropriate in some contexts, but since we can't know the full context, I'd suggest such words be underweighted in the Big Picture.