Krugman on Portugal and the Migration Death Spiral

Paul Krugman comments that Portugal can be a situation where its aging population, combined with a large outflow of younger people due to high unemployment, can lead to an ever worsening financial situation where fewer workers are left to support a larger debt and non-working population. (Note, the key factor here is the migration, not the aging.)

That pretty well describes the picture with Puerto Rico, with a large segment of its working age population moving to the mainland United States, l...