Dems ran a disastrous and out of touch campaign.
1. As many have already pointed out - Biden promised to be a transitional candidate. Who then attempted to break that promise, denying Dems a traditional primary and full campaign cycle.
2. Telling people the "economy was great" - when wages have by no means come close to making up the difference in cumulative inflation, and for those whom it has, most were upper-middle class and above, who weren't hurting anyway. They handed the working and middle class to the Republicans on a platter, while pleasing their donor class and appearing completely out of touch.
3. Continuing "out of touch" - Trump was jumping on popular podcasts, pulling his stupid McDonalds stunt, etc. Kamala was stacking her stage with celebrities and elites. Not a good, and definitely not a populist look.
4. Touting their Liz Cheney endorsement. No, she is not in fact "popular outside of MAGA circles." Maybe with a few old-school neocon republican warmongers. For anyone on the left with a shred of integrity, the bare minimum she could add to Kamala's campaign was a decrease in enthusiasm. Add to that, Dems were already hearing rumblings of a loss in support from Muslim communities over the Gaza genocide. Cheney is the LAST person you want on your side when trying to keep the approval of people concerned about US backing and interventions in the Middle East. And guess what? Dems lost Dearborn, MI. ------- Dearborn.
5. Lies and hyperbole. "Trump called for a bloodbath!" He threatened to execute Liz Cheney! Whatever. As Bill Maher put it, you don't have to lie to me to make me dislike Trump. He says enough repulsive crap as it is. Example 1, he was clearly talking about an economic bloodbath, example 2, about warmongers not having to actually fight, etc. You just insult voter intelligence and undermine your own credibility. It makes Democrats look like liars and reinforces Trump's goal of undermining traditional media.
6. "It's the economy stupid."
7. "It's the economy stupid."
8. "It's the economy stupid."
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Average American voter hasn't got the memory of a goldfish in a bowl of vodka - so you're saying the problem extends beyond the brain?