I don't think the Republicans have a more coherent philosophy than the Democrats. Just a simpler one, with no sense of shame, embarrassment, or qualifications.
But yes, the Democrats have a lot of internal contradictions that are easily perceived as weakness by not just the Republicans, but also, the many "swing" voters who vote based on the strength of the economy, the charisma/gravitas of the Presidential candidates, and the perceived "toughness" of the Commander-In-Chief.
Bottom line is: the American political process is based on wealth, power, confidence (manufactured, more often than not), and the corporate sponsorship and ownership of the media that promotes democracy-by-sound-byte. In this context, the better your party is at generating simple, memorable sound-bites on a regular basis, the more of an advantage your party has throughout the election season.
Politics is a business in the US; that much is clear. The Republicans figured that out quite some time ago. The Democrats haven't fully gotten the message yet.
This post is a text-book example of what often plagues the Democrats electorally.
The success of any campaign hinges on the grassroots. It's the grassroots that spreads and personifies the party's message; they are representative of the nature of the ideologies the omnipotent party leaders in Washington are asking voters to believe in. When your most articulate followers are out in their community saying things like "Liberalism is the superior ideology, most people just aren't smart enough to know it" and "Republicans win because voters are sound-bite craving automatons". - people will eventually grow bored of your superiority complex and cease to take you seriously.
Simply put: In politics, s**t rolls uphill.
Simp