Nuclear reactors could provide power almost indefinitely. Greenhouses could maintain plant life. Animals could be bred and slaughtered. A quick survey would have to be made of all the available mine sites in the country, but I would guess that dwelling space for several hundred thousands of our people could easily be provided.
A computer could be set and programmed to accept factors from youth, health, sexual fertility, intelligence, and a cross-section of necessary skills. Of course, it would be absolutely vital that our top government and military men be included to foster and impart the required principles of leadership and tradition. Naturally, they would breed prodigiously. There would be much time, and little to do. With the proper breeding techniques and a ratio of say, ten females to each male, I would guess that they could then work their way back to the present Gross National Product within say, twenty years.