“The big dog” as Tom Renney refers to Jaromir Jagr, can’t pull the Rangers’ sled. His arm is as weak as the supporting cast, which can’t help him enough, just like in turn, Jagr isn’t healthy enough to carry the team as he did through February last season.

The second line center, Matt Cullen, is a shooter mostly, not much of a playmaker, which makes production from that unit problematical. Brendan Shanahan is getting worn down from a too-heavy workload, which Renney has deemed necessary because the third and fourth lines never score.

Sometimes they don’t even pick up their men and get the puck deep, which is the minimum third and fourth lines are supposed to do.

If the Rangers overall performance seems to ebb and flow with losing streaks following winning streaks, it’s not effort or self-satisfaction that keeps dragging this team backwards but a shortage of depth through four lines and three pairs on defense.

The Rangers have a group of players not capable os sustaining their efforts except in short bursts, which makes this a roster screaming for a trade. And it’s a good question what the first priority should be — a center or a defenseman and what they have to offer to get what they need — but unless some upgrades come, the Rangers are going to have a hard time making the post season.

That somehow, they are still in playoff position despite off-seasons by Jaromir Jagr and Henrik Lundqvist, is a reflection of the very thin margin between very thin teams in this new, capped, NHL world.

But the Rangers are not, as surrently constituted, better than any of the five teams — Boston, Pittsburgh, Washington, Tampa Bay and the Islanders — who occupy spots nine through 13. Some of them will find ways — internally or othewise — to improve in the second half, and unless the Rangers do, too, this rebirth dies after only one season.