It has nothing to do with messaging or strategy. Americans have been conditioned from birth to HATE liberals. The only thing that seems to be able to overcome it is to crash hard enough. 2008 was hard enough to get some power back but Americans also have pathetically short memories. 2 months of ramped up agitprop was enough to make them completely forget the shit that the Bush admin did and hate liberals again. We need a crash that lasts long enough that America never forgets.
If that were inevitable, then dems wouldn't have won 6 of last 7 popular votes.
No spell is unbreakable. What Dems have lacked is a credible counterargument in terms of economic policy, and have not been able to control narratives around this issue in a generation.
Where dems have succeded in this is on social issues, particular around racial, gender and sexuality equality.
They need to focus on this and get back the prosperity trust that FDR built, but have been steadily losing since Reagan.
The R platform is built on fraud and lies. It can topple if given the right kick.