Speaking of vote volumes, using numbers reported to date.
2020
2024
Difference
Biden
81,283,501
Harris
67,203,507
14,079,994
Trump
74,223,975
Trump
72,015,286
2,208,689
155,507,476
139,218,793
16,288,683
This tells only part of the story, but it tells me that the core Trump support, even while down slightly, was loyal to him (duh, look at the flags people fly) enough to overcome the absolute mess of a process the Democrats decided to use. Harris has never been popular nationally and the lack of turnout illustrates some of that.
There are other lessons to be learned about messaging during a campaign, but in my lifetime the Republicans have been far superior in their approach to talking about issues. They keep it simple and they stay together.