Progressives/libs which would include Dems/RINOs don't have much pressure to hone and focus their message, that's their problem. Everything that sounds great and is big government...is great. Big government is the solution to everything. The ideologically opposed groups (conservatives/liberatarians) are under an electron microscope and face intense scrutiny with every twitch. They have become jaded with "the system" and are skeptical of everything. Those differences underlie a lot of what happens and how both sides view the media. Just my take.
The messaging for conservatives is so well-honed because the media (and of course, the Board Left) is out to get us. Dems enjoy a privilege which permits everything that they do or say to be afforded a presumption of moral purity, since there is no firmer proof of its good-intentions than that they themselves said it. The media is happy to echo these sentiments, and carefully nurtures the Dems* and their message, like an egg which is dangling precariously on the edge of the nest beneath the warming comfort of the brooding hen. So full of promise and purity: nature's perfection in the palm of your hand.
Conservatives, meanwhile, are subject to constant scrutiny. Everything they do, say (or better, don't do, and don't say) is evidence of their moral failings, intellectual inferiority and their well-documented hatred of school children, the environment, international football, public sector employees, young people, old people, young people, the middle aged, gay people, bisexuals, all other previously unenumerated minorities (past, present and future) and in fact the majority of people that are women. For example, when asked an arbitrary and stilted question about history, any correct, responsive answer occurring before 1865 is evidence of endorsement of the institution of slavery, because obviously. The messaging is better because it is constantly under multilateral assault from phalanxes comprised of the forces of empathy, understanding, and of course, true and just compassionate intellect. The hottest fire forges the strongest steal. If you think about it, my fellow conservatives and I are the real victims (P.S. Am I doing it right?).
When Dems' message has to face the voting public, it is kind of like Dook in the NCAAT. All season long coddled by ACC refs and lulled into a false sense of superiority, but when it comes to the big dance, a first round knockout to Mercer 20 minutes from campus.
For one instance among many, how many times would Joe Biden's career have been over were he a Republican? The Dems made him Vice President.