I, like you, am very critical of the Trump administration’s decision to ban travel from Chad. As you note, it undermined American-Chadian counterterrorism cooperation.

However, I’m not aware of evidence that Chad’s reduced counterterrorism cooperation with the United States contributed to the recent American deaths in Niger. The US-Chad cooperation focused on Boko Haram in southeast Niger, while the recent attack took place in the west of the country. And it looks like an ISIS affiliate called Islamic State in the Greater Sahel was responsible.

Chad’s operations in Mali focus on Al Qaeda in the Islamic Maghreb, which is mostly in northern Mali, away form the Niger border. The main Western power assisting African forces in that campaign is France, not the United States, and I haven’t seen any indication that Chad has reduced its cooperation with France.