His argument is that a) the poorest in the US are maybe worse off than we think, and b) we should rethink the "cosmopolitan” ethical rule that places an equal weight on foreigners as co-nationals. Of course, he says, we shouldn’t totally disregard foreigners, we just have lower obligations to them, and greater obligations to people in the same nation as us. Which is all fine and everything, but its also a bit of a straw man. The interesting question, if we can agree that we have lower but not zero obligations to foreigners, is *how much* lower are our obligations to them?
In one of my favourite ever blog posts (now offline, but summarised on Dani Rodrik’s blog), the anonymous blogger “YouNotSneaky” calculates how much you have to value the welfare of a foreigner in order to oppose immigration (or “How much of a jerk do you have to be to oppose immigration”). The answer is you need to think that our obligation to foreigners is less than 1/20th of our obligation to co-nationals in order to oppose any immigration. Personally, I’m not at all comfortable with that low of a weight, but I suppose your mileage may vary.
In principle you could make some kind of similar calculation with regards to foreign aid, but I’m guessing that the less than 0.7% of GDP we so generously lavish on the global poor isn’t anything close to how much we would spend if we were actually really anywhere close to being "cosmopolitan prioritarians” and treating our obligations to foreigners as equal to those to co-nationals.