Sadly, I think that you are wrong that Trump doing as well as Romney would count as “winning,” since Romney did lose. Even if only 10% of the population ever changes their mind, or more likely, 10% can be persuaded to not vote, well, you need that 10% to win! So I suspect that even though the (D) and (R) candidates for President are probably locked in for a large % of the popular vote (it’s hard for me to imagine ever not voting D, that’s for sure), they happen to lock us into endless marginal races, in which every little bit of advertising matters.

I like the analogy though – there is a similar crisis in autos. Yes, a lot of advertising is one brand vs. another, but in an era of car sharing, urban living, and student loans, the auto companies have to convince a new generation of consumers why they even bother to own a car, yet alone their car.