Presidential Proclamation 9645, an Executive Order issued by Trump that is commonly known as Travel Ban 3.0 (and awaits Supreme Court review), listed various countries whose nationals would not be allowed U.S. visas or entry. (At least, not without a special waiver, few of which have been granted.) The Republic of Chad was on that named list of countries.
Now, the Trump administration has announced that, starting April 13, 2018, Chad is being removed from the restricted list. (This was mentioned in a document called "Presidential Proclamation Maintaining Enhanced Vetting Capabilities and Processes for Detecting Attempted Entry into the United States by Terrorists or Other Public-Safety Threats.")
The decision was apparently the result of cooperation by Chad on stricter security procedures. The review process included a U.S. site visit, meetings with officials from Chad, and "marked improvements in [Chad's] identity-management and information-sharing practices" to avoid issues such as use of false passports and similar documents.
No other countries were removed from the list, though the Proclamation suggests that others might be making progress in that direction.
Citizens and nationals of Chad can expect to resume normal visa applications and travel to the United States. Details of any changes in procedures have not yet been announced; but expect the possibility that you may need to apply for a new passport.
Effective date: April 13, 2018