Cite the source for "access to healthcare" as a "very significant factor" in US life expectancy? We have pretty good numbers on the mortality cause differences between the US and other countries and they don't align with this claim (unless you're doing some bank-shot argument about how access to health care makes our car crashes more lethal or something).

You'd want to be looking for a scholarly source that puts numbers on this. It's been done! As I noted elsewhere on the thread, the study we're commenting on is based on 1990s numbers about differing mortality of the uninsured. But here you're looking breakdowns of all mortality causes and tying them to insurance, a trickier proposition. Will be interested in whatever you come up with.

https://www.ncbi.nlm.nih.gov/books/NBK62376/