You are right... it was speculation for me to say that. However, that speculation is based on a LOT of studies on Americans.
Americans are much more individualistic than most people in the world (lots of studies on this). America was founded by immigrants looking to make their own way without a lot of interference from others.
We had the first wave of immigrants from England, then Germany, then Scotch-Irish, followed later by more Germans, Polish, Irish, Italians, and others. The latest wave is from Mexico and the immigrants from Mexico are driven by the same ideals (leave the past behind and look for opportunities in America).
Even though the immigrants came from many different ethnic backgrounds, they all shared the pioneering spirit of leaving their family, friends, and love ones behind, and make thier own way in America). Americans have this bred into us.
The Democratic message is a socialist message. It talks about taking from the producers and giving to the non-producers. It talks about the government providing services, jobs, and opportunities (instead of people obtaining their own services and making their own way). The Democratic message is fundamentally anti-American and won't sell in America (as of today anyway).