Opinion by Matthew Dowd, ABC News Political ContributorIn analyzing communications, connections and acceptance by voters in politics or even consumers in business, the most important element is the "brand".The brand being what is the core value encapsulated in the candidate through which voters accept or reject what is communicated.In politics, while mechanics/tactics (advertising, mail, grassroots, etc.) are important, they pale in importance to the brand. And what is crucial in any campaign is protecting at all costs the brand of the candidate –- the authentic core of who the person is, why they are running, and how they would lead. Obama's brand is new to the political marketplace and it is especially in need of protection by him and his campaign. What is his brand?From my perspective it is something that involves a new kind of politics, something that doesn't involve political expediency, something that gets past the spin of Washington, something that involves truth and inspiration in order to get the job done.That is why I believe Obama and his campaign made a blunder flip flopping on public campaign finance for the general election. Obama had said for many months he would abide by public financing in the fall and now has decided against doing just that. As Liz Sidoti of Associated Press wrote, "Barack Obama chose winning over his word."Not a good thing at all for his brand. Is it lethal? Probably not, but it's a mistake.The more interesting thing is that he didn't need to do this. The way the system works he could have outraised and vastly outspent McCain in the next 90 days before the Democratic convention because primary dollars are still in place. After the convention, he basically only has eight weeks left and spending a little less than $90 million dollars (which is the public finance amount) effectively is going to be all but impossible.The urban myth in presidential politics (which media consultants don't like to hear) is that paid advertising is key -- it absolutely isn't!The most important part of the campaign is not gross rating points, but the narrative in the free press. And Obama could have gone along with public financing and still raised millions of dollars for the DNC which could conduct grassroots organizing on behalf of the entire ticket. And if you look at the polls generic Democrats do much better than Obama himself.Politically, on behalf of both his brand and the effective conduct of the campaign, it was an error for Obama to choose tactics over truth.By the way, isn't that exactly why most people in this country are upset at the current administration????