grasp at a straw

To make a desperate attempt to salvage a bad situation. A: "But what about all those times I took the trash out when you hadn't even asked me to?" B: "That has nothing to do with why you're in trouble now, so stop grasping at a straw." The government is really grasping at a straw now in its attempt to defend the controversial legislation. A: "I've started going to a psychic to help me figure out how to salvage my marriage." B: "I think you're grasping at a straw, Mike."