That is the only lesson they are ever capable of winning. If they win, it's because they were like the Republicans so they should be more like the Republicans. If they lose, ti's because they weren't like the Republicans enough.
The Democratic base, and i say this as someone who willingly voted straight D ticket and has for a long time, keeps trying to kick the football and the Democratic Party keeps yanking it back at the last second. Every time.
Their job was to demonstrate that they knew what was happening, had a plan to address it, and their plan was being blocked by politicians who had none of that. They didn't even try and i don't think they ever really wanted to. Same with Obama bailing out the banks and leaving the regular people with the bill during the financial crash of 2008. (That was in no small part Bush's fault, but he didn't even try something different.)