So I dug into this, and the following excerpt is the only piece of information related to the claim in question:

In the run up to the 2020 election, religious conservative public figures – for example, Rick Perry – claimed that Donald Trump was anointed by God; Perry called him “the chosen one” (see Djupe and Burge 2019). The head of Trump’s Evangelical Advisory Council, Paula White, went a bit further: “To say no to President Trump would be saying no to God, and I won’t do that.” In May 2019, 21.4 percent of Protestants believed Trump was anointed by God to be president, as did 29 percent of evangelicals, and a majority of Pentecostals (like Paula White). Belief in Trump’s anointing increased considerably closer to the 2020 election (Djupe and Burge 2020; Edsall 2020).

Here are the original sources of the claim:

1. Djupe and Burge 2019
2. Djupe and Burge 2020
3. Edsall 2020 (archive link)

I’ll keep editing this comment as I get further into it.

Edit 1: added archive link for Edsall 2020

Edit 2: fixed the link for Djupe and Burge 2019

Edit 3: Here is an archive link to the Economist article.

Edit 4: relevant quote from the Economist article:

In a survey conducted by Mr Djupe shortly before the election, three in ten Americans believed Mr Trump “was anointed by God to become president”.

Edit 5: Conclusion

It seems as though the Economist article, and therefore the Raw Story and various other articles referencing it, are not correct. I’ve looked through a couple dozen resources at this point, and I cannot find any publications from Djupe or Burge substantiating this “30% of Americans” claim. However, I did find

However, I did find this:

Other surveys have shown similar results. A 2020 Pew Research Center survey asked Americans, not just church-attenders, about God’s role in recent presidential elections. They found that 32 percent of the more than 6,000 respondents, a sizable minority, believed Trump’s election must be part of God’s overall plan—though only 5 percent of those respondents believed God chose Trump because of his policies.

So maybe the 30% finding was from Pew after all? I’m going to send all this to the Economist to ask for clarification.