While there is a political point-scoring cum pissing contest going on over whether the President should have explicitly commemorated the deaths of 4 US servicemen in Niger, a more significant underlying question has yet to be answered, as pointed out here by Jim Wright:
Let's back up a bit.
How many of you knew there were US forces in Niger? What's their mission? What are we doing there? https://t.co/fW6NXe7cec
— Stonekettle (@Stonekettle) October 15, 2017
It is possible that the reluctance of the administration to publicly commemorate the deaths of the service members is because, officially, their mission did not exist, and they should not officially have been anywhere near the country. Which would not exactly be a new development in the modern era. The USA has been engaging in covert actions in dozens of countries. Some of those covert operations may never be revealed, they will stay officially non-existent.
All of this is part of the Faustian bargain that Congress and the Senate struck with the Presidency starting in the Cold War, where they abdicated oversight of overseas military command to the POTUS. This gave them the best of both worlds. if the overseas involvement was seen to be successful, they would praise the military, wrap themselves in the flag, and move closer to the POTUS at press conferences and photo-ops. If the operation was seen as unsuccessful they would be able to accuse the POTUS of “military misadventure” and walk away from the outcome.