I don't really think people withdraw their support, there was never the support in the first place. Here is the thing, many people don't like Trump but they will rather put their last vote on Trump than wasted it to a woman to become their president because the government already becomes a joke, Biden was sick and like a dead person that is trying his best to leave the office and face his life but many people weren't please with Kamala been the face.
Nah, Trump had a lot of support. The last administration failed in so many ways, so people wanted something different, and that was why it was easy for Trump to have so many supporters. Also, Trump knows how to portray people as the cause of all the problems in the country. He did it in his first term, and it worked, and it worked again this time around.
I agree, if Kamala were a man, a white man, especially one who has achieved what Kamala has achieved in her career and had a campaign like Kamala's, then they would have won the election. But that does not mean Trump didn't have supporters.