Why is the US perpetually short of nurses?

There is an outcry in the United States that we're facing an urgent nurse deficit that threatens the safety of individual patients and the nation's health as a whole. Consider arguments from two Times editorials. "The nationwide shortage of nurses is likely to reach crisis proportions…. There is not much chance for permanent relief until the nursing profession is made more attractive to young people through better salaries, working conditions and public recognition," one reads. In another, titled "We Need More Nurses," Alexandra Robbins warns of dire consequences in the absence of a larger nursing workforce: "The more patients assigned to a nurse, the higher the patients' risk of death, infections, complications, falls, failure-to-rescue rates and readmission to the hospital—and the longer their hospital stay."