I'm gonna paraphrase Jon Stewart from sometime in the early 00's; "Never underestimate the power of the Democratic Party Operation: We're Gonna F**k It Up Again."
The Democrats, as a broad generalization, are really good at governing. They propose legislation then make compromises in order to do the greatest amount of good. They understand that you have to pay for government, and that means you have to have taxes.
They suck at campaigning.
The Republicans suck at governing. They cut taxes but increase spending. They increase spending in just certain sectors of the economy that benefit small groups. They won't make compromises. And they won't admit something didn't work.
But they're great at campaigning.