The precise number of countries whose nationals are barred is not clear.  The presidential action of this month identified 39 countries. Not included in Palestine and Gaza; there can be others added. This posting addresses the bureaucratic reasonins for the bans and provides a summary of 39 countries.

The goverment bases its travel bans on the grounds that visa overstays, corruption and internal instability make it difficult for the State Department to screen visitors to the United States.  One might argue that the challenges to screening are vastly exaggerated.  There have been only about five fatal foreign-born terrorist attacks by these nationalities since 1980. (Since 1980 there have been at least 700 mass murders of at least five persons.) It might well be that other measures to reduce overstays could be applied.

Here is a comprehensive government document, showing how the 39 countries  accumulated over several months.

Most countries are small to very small, and the impact for them on the U.S. society and economic is extremely low. However, Nigeria, with a population of about 233 million, is included.  Most of the countries have stable governments and about half are middle income countries – neither impoverished nor with seriously compromised central governance.

Roughly half of the affected countries have partial, the other half full suspensions.  Partial suspension means that temporary business and students visas are not issued, but an array of more specialized visas is permitted. Full suspension means that virtually all entries are barred.

Visa overstays. The median global overstay rate for all countries appears to be about 2.5%.  The median overstay rate among the affected counties for overstaying business, personal and tourist visas (B-1 and B-2 visas) is 9.95%. The median overstay rate for student visas is 18.43%. the precision of these figures obscures the reality that a lot of intepretation goes into overstay rates.

Administrative failures. Corrupted or otherwise deeply flawed government records (for instance criminal records); corrupt educational certification processes; corrupt passport issuance, refusal to accept deportees who are citizens of the country, and other criteria. Virtually all affected countries are faulted in this area.

Security-based risks. Where State Department screening cannot effectively control for state collapse, terrorist organizations, armed conflict, kidnapping risks, transnational criminal activity, etc. Half of countries fail here. Again, the number of terrorist acts in the U.S. by these nationals is vanishingly small — about 5 in 40 years.

What about the truly major country on the list, Nigeria? It has a business visa overstay rate of about 5% and a student visa overstay rate of about 12%.

List of countries: country name, partial or full suspension, business visa overstay rate if known, and population. Example:  Senegal is partly banned, has a business visa overstay rate of 4.3% and a population of 18,8 million.

Africa — Angola (P; B‑1/B‑2 14.43%; pop. ~37.9m); Benin (P; 12.34%; ~14.6m); Burkina Faso (F; 9.16%; ~23.4m); Burundi (P; rate n/a; ~14.0m); Chad (F; rate n/a; ~19.5m); Côte d’Ivoire (P; 8.47%; ~31.9m); Equatorial Guinea (F; rate n/a; ~1.9m); Eritrea (F; rate n/a; ~3.7m); Gabon (P; 13.72%; ~2.5m); The Gambia (P; 12.7%; ~2.8m); Libya (F; rate n/a; ~7.5m); Malawi (P; 22.45%; ~21.7m); Mali (F; rate n/a; ~22.4m); Mauritania (P; 9.49%; ~5.1m); Niger (F; 13.41%; ~28.2m); Nigeria (P; 5.56%; ~232.7m); Republic of the Congo (F; rate n/a; ~6.2m); Senegal (P; 4.3%; ~18.8m); Sierra Leone (F; 16.48%; ~8.9m); Somalia (F; rate n/a; ~19.0m); South Sudan (F; 6.99%; ~11.5m); Sudan (F; rate n/a; ~50.4m); Tanzania (P; 8.30%; ~68.6m); Togo (P; rate n/a; ~9.3m); Zambia (P; 10.73%; ~21.6m); Zimbabwe (P; 7.89%; ~16.6m).

Asia — Afghanistan (F; rate n/a; ~43 m); Iran (F; rate n/a; ~90.6m); Laos (F; 28.34%; ~7.6m); Myanmar/Burma (F; rate n/a; ~54.1m); Syria (F; 7.09%; ~23.2m); Turkmenistan (P for immigrants only; rate n/a; ~7.1m); Yemen (F; rate n/a; ~40.6m).

Western Hemisphere — Antigua and Barbuda (P; rate n/a; ~0.09m); Cuba (P; rate n/a; ~11.1m); Dominica (P; rate n/a; ~0.07m); Haiti (F; rate n/a; ~11.8m); Venezuela (P; rate n/a; ~28.3m).