There has been a lot of focus on the New York Rangers' desire to add an impact forward to their roster this offseason. Trade rumors have swirled about their potential interest in Brady Tkachuk of the Ottawa Senators if he were to become available. A top-six forward is the ultimate goal, but it is far from the only need on the roster. Arguably, the most glaring need is at the blue line. The Rangers have an elite defensive pairing of Adam Fox and Vladislav Gavrikov as their top line. When on the ice together, there aren’t many teams that have a better duo anchoring their defensemen depth chart. Head coach Mike Sullivan knows what he is going to get when Fox and Gavrikov are on the ice together. Where the problem truly lies is on the second line, with the depth behind their top two needing improvement.…