I'm not sure how my argument changed, or what you think my original point was. By saying Trump is right in regards to his "who cares?" comment, I was making the point that Warren's response is not going to make any difference to anyone that matters in how they view Trump. Nobody important cares that Trump got it wrong, or that he's the one who actually made an issue out of it, that's not how he's evaluated. Everybody who already despises him will have got their day's moment of outrage mixed with satisfaction before moving on to the next thing, while his supporters will just see the entire episode as evidence of Warren's dishonesty and further evidence of their hero's don't-give-a-feck approach to his rivals, which they love. For those who actually matter, i.e. anyone still unsure about Trump, it's a non-issue - if they've watched Trump engaging in these petty disputes for years now and been proven wrong countless times, and are still on the fence about him, then it's clear they have other priorities than worrying about Warren's heritage. They don't care about it. All Warren's response does is engage Trump in an area where he's most happy; as you say, "it's worked for him so far."