The NY Rangers need left defensemen. More importantly, they need good, young left defensemen with term that can be a part of the long term plan. They have the pieces to make a trade that would take advantage of teams with cap trouble. One of those teams is the St. Louis Blues. Targeting Vince Dunn should be a priority for the Rangers.
STL friend @KevinLorenz is convinced that Vince Dunn is a cap casualty for the Blues. I have no idea how a trade would look but Dunn (to be 24 in OCT) has had a solid NHL start.