In my view: the lack of engagement with the historical record. This topic - and the meaning and expected outcomes of the wording for the amendment - were discussed and debated as part of the open record. Senator Cowan thought the phrasing created a loophole for birthright citizenship, and the amendment creators explicitly, overtly, repeatedly agreed with his interpretation of the phrasing and defended it as deliberate policy.

As I posted elsewhere, you can read some of this for yourself: https://global.oup.com/us/companion.websites/libertyandjusti... (CTRL+F "If my friend from Pennsylvania" for a quite pertinent line).