When candidates respected their audience's intelligence...

 I do not believe that everything's going to — in a hand-basket. I think anthropology doesn't change much in the aggregate—moderns are quite as self-interested as ancients; contemporary American political unrest is not on the scale of the 1860s or even the 1960s! But I do think political dialog has fallen off a cliff. I haven't bothered watching a presidential debate since Obama and Romney squared off in 2012 and even two of the most intelligent people to contend for the office in recent history utterly failed to say anting noteworthy or even helpful (I've kept up with the content of presidential debates since; I just haven't wasted time trying to be entertained by it as it hasn't been worth the effort).

This quote from Eric Jaffe's The King's Best Highway suggests it was not always so: examining Lincoln's speech to an East Coast audience in February of 1860 in which he took up Douglas's claim that the Founding Fathers had not intended the federal government to sound in on the issue of slavery Lincoln actually dug through legislative precedent for his audience, citing the voting records of the signers of the Constitution and interpreting whether those records supported the idea that they believed the federal government had a right to speak to state decisions on the issue of slavery.
"All in all Lincoln had found evidence that twenty-three men who signed the Constitution had taken a political action endorsing the federal government's right to control the spread of slavery. Twenty-one of these, a clear majority of the thirty-nine, had voted to actively stop such a spread. Of the sixteen signers for whom Lincoln could not find direct voting behavior—including 'Dr. Franklin, Alexander Hamilton and Gouverneur Morris'—all but one were known to oppose slavery. It was reasonable to conclude, then, that of the thirty-nine men who signed the Constitution—men who 'understood this question just as well, and even better, than we do now'—at least thirty-six would certainly, or very likely, agree that the government can and should interfere with slavery's expansion."
What's more, "two editors tasked with preparing footnotes for a published version of the speech needed three weeks and the help of several historians... just to verify the facts."
Lincoln didn't just offer counter factual statements to Douglas; he offered legislative evidence! And this as part of a complex argument in which he agreed with Douglas's declaration that "Our fathers understood this question [of whether the federal government had the right to speak to the issue of slavery] just as well, and even better, than we do now" but then deconstructed Douglas's argument based on the evidence Lincoln offered. He seemed to have a lot more respect for his audience's intelligence than anyone who's offered presidential debate during my adult lifetime...