I think you overestimate the ability of the public to understand or appreciate the danger of socialism. It was easier when the Soviets still existed, they were a direct threat and it was relatively easy to rally people against extreme leftists. (to say nothing of leftists bombing buildings and kidnapping people in the 60’s and 70’s)
However since the collapse of the Soviet Union it’s become increasingly difficult to campaign against themes like socialism or communism. Part of it is that conservatives ceded control of the government schools to the left decades ago. We’re now reaping that reward, kids graduate predisposed to oppose capitalism if they even know what it is. Worse, they graduate expecting government to “do something” about every problem because that’s what they’ve been taught for 12 years.
We used to be able to rally some of these people to our side based on shared hatred of the Soviet Union or shared ties to what remained of the church or capitalism. These days those ties have been destroyed and it’s going to take more than a campaign to fix the problem. How can you campaign against something that people don’t recognize as a problem no matter how much you tell them it is?
Certainly you make some good points that I agree with, but the idea that these letters do not matter unless the majority of the public at large understands them is where you are wrong. They matter, meaning they should be talked about - not because they are a magic bullet.
A lot of things matter to a degree in an election - a flip of 2-3% can make a tremendous difference. If Hillary can be radicalized, then that could be 2-3% easy. Could cost her some Wall Street money up front also.