Proclamation 9723--Maintaining Enhanced Vetting Capabilities and Processes for Detecting Attempted Entry into the United States by Terrorists or Other Public-Safety Threats, April 10, 2018 [open pdf - 221KB]
From the Document: "Now, Therefore, I, Donald J. Trump, by the authority vested in me by the Constitution and the laws of the United States [...] find that the entry into the United States of the nationals of Chad, as immigrants, and as nonimmigrants on business (B-1), tourist (B-2), and business/tourist (B-1/B-2) visas, no longer would be detrimental to the interests of the United States, and therefore hereby proclaim the following [see document]."
Pres. Docs., 2018 DCPD No. 00231
Federal Register: http://www.federalregister.gov/