America, the Underpopulated?

(Comstock)

A recent editorial in The New York Sun argues that all this political bickering about immigration among Republican candidates misses an important truth: America is actually underpopulated. From the article:

[N]ot a single Republican candidate has spoken up for the idea that America is an underpopulated country. In terms of population density, it is, at 83 persons a square mile, an impoverished country, barely a quarter of the rich density of China, which is running way behind India. America just has enormous room for population growth.

And a desperate need.

What do you think, readers?  Is America under-populated? Would Montana and Wyoming, for example, benefit from a few more people?

(HT: Paul Kedrosky)