Previously I would have said buying election results. But apparently the electoral college makes it surprisingly cheap. Musk buys twitter for 44 billion dollars and yet he only needed a quarter of a billion to buy the American government.
https://www.axios.com/2024/10/31/democrats-republicans-ad-sp...
Way more billionaires supported Kamala vs. Trump (83 vs 52).
But yes, there was also simply a lack of energy in the D voter base in 2024. No amount of spending can recover disengaged voters who simply dismissed everyone as "equally bad".