About 10 or 20 minutes after I posted the story, I found the actual study by Dennison University that is the basis of many of the claims.

Here is the /official/, paywalled, abstract only link on Cambridge's journal or study publishing site:

https://www.cambridge.org/core/elements/abs/full-armor-of-god/2B21DC6F17E88C6DF7275F45A66DF104

And here are various links to the full study provided by scientists amd volunteers who believe information should be freely available:

https://annas-archive.org/md5/da76eb110551fd4028c9c0a8e185f0ce

I have not had enough time to read it but given that 40% + of American adults believe in the Biblical Creation narrative of the world and do not believe in evolution, I'm pretty confident the 30% figure refers to basically American Adults, ie potential voters, in this context.

This article has more detailed information on the surveys conducted. It seems to be about a third of US adults.

https://bigthink.com/the-present/was-trump-anointed-by-god/

Interestingly, while skewed heavily towards Republicans, some Democrats also hold this position and a much smaller percentage overall believe he was selected because of his policies.

It doesn't say. That and the fact that this is reporting on other reporting, a kind of "reaction video" of journalism should be enough to ignore that number.

30% of Americans that were willing to take the survey... So the most enthusiastic voters...

It's 21 percent of weekly church going Protestants. Unless OP cares to actually share the operative part of the book. That's the number in the interview we've been able to find.