Is the agenda voters think politics is "about" actually manufactured by campaigns, or do strategists mostly ride waves they didn't create?
The premise here is that strategists elevate whatever divides and mobilizes, so the issue agenda the public experiences is partly an artifact of what campaigns choose to push. I think the first half of the question has a cleaner answer than the second, and the answer complicates the premise a little.
On measurement, yes, there is a whole tradition built for exactly this. Agenda-setting research going back to McCombs and Shaw in 1972 compares the issues emphasized in coverage against the public's own "most important problem" rankings, which pollsters have tracked for decades. So the gap between the elevated agenda and what people say actually matters to them is one of the better-measured things in the field.
Where it gets interesting is the causal direction, and this is where I would push back on the strong version of "manufactured." The issue-ownership and saliency literature (Petrocik, and van de Wardt, de Vries and Hobolt on wedge issues) finds parties mostly emphasize issues they already own and that already have public traction, rather than conjuring salience out of nothing. A fair amount of longitudinal work finds the reverse arrow too, with public concern driving coverage rather than the other way around. So strategists look less like they invent the agenda and more like they amplify the divisive parts of an agenda that events and existing loyalties already handed them. Still a distortion, but a different one, with a different fix.
Which points at what I think is the actual gap. Divisive issues get elevated because someone profits electorally from elevating them. Consensus issues do not get actively suppressed so much as orphaned, because no party, donor, or outlet gains a comparative advantage from raising something both sides already agree on. The absence looks structural, not conspiratorial.
Two questions I don't have a clean answer to. Is there work that measures suppression specifically, meaning consensus issues that had public salience and then got deliberately pushed down, as opposed to issues that were simply never picked up? And on reach: is there any actor with both a mass audience and an incentive to put agreement on the agenda, or is that combination basically vacant?