Caulker has been poor in his last couple stops. However, he has to realize that he has to be at his best here. Saints owe him precisely nothing...he won't get playing time because he came at a high fee, and he won't get playing time because we simply have no options. If he doesn't perform, he's at best our fourth CB, and could find himself out of the matchday lineup entirely when Gardos returns or if one of the kids progress. And if we cut him loose at the end of the loan after being used sparingly, good luck to him getting another Premier League gig, because I don't see QPR bouncing straight back.
If he can look at all that and still doesn't perform, either the player with Swansea was a mirage, or he's too dumb to trust for a club intending to go somewhere. For just the cost of wages, worthwhile risk on our part to find out whether one or both or those are true, or if there's still a good CB in there.