An advertisement saying "It's not racist to impose limits on immigration" isn't dog-whistling, and I don't think anyone claims it is.
Yet according to the Wikipedia article you linked, that was claimed to be "the classic case of dog-whistling." So I find this discussion frustrating because you don't seem willing to come to terms with how the phrase is actually used.
What the page says was called the classic case of dog-whistling is a whole advertising campaign.
I checked what Goodin's book (cited at that point in the Wikipedia article) actually says. It doesn't reference any specific advertisements in the campaign, and in particular doesn't describe the specific one you picked out as dog-whistling. It does, however, say this:
...The fact that the practice is noticed, that it has acquired a name and a bad press, suggests that the message is not literally inaudible to others beyond its intended target. They have noticed it
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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