I believe that the US should in fact conduct more research in to mini-nukes because it can help us identify if other countries are using them or planning to use them. I belive that if the US has a grasp on how the production of mini-nukes occurs we can be better equiped to handle them if we come across them.
If you haven't it was a tactical nuke system which was pretty much just a small nuclear warhead on the end of a small rocket. It was extremely inaccurate and was eventually defunded because of how stupidly unnecessary it was. It was designed to take out lines of tanks during the cold war, but could be used to take down an entire city. WHY DO WE NEED THIS?!? Not only would this devastate the land with nuclear fallout, but were it to be used for defense it would surround your city with deadly radiation. Were it to be used for offense you couldn't advance because there's deadly radiation in front of you. WHY?!? We don't need these.
Nuclear weapons on this world have too high of a consequence. No country should possess any nuclear technology. Mini-nukes themselves aren't even needed by the US. If it were to be developed, there's a very low chance that they would ever be deployed. The US has better things to spend their money on.