knock the props out from under
knock the props (out) from under (someone or something)
1. To undermine, weaken, or destroy something. The stock market crash knocked the props out from under a huge number of investment firms across the nation. Tom knocked the props from under our proposal during the meeting.
2. To erode or undermine someone's self-confidence or sense of self-worth. Losing her job really knocked the props from under Sarah. I hope she comes out of this funk soon. Don't let the boss's comments knock the props out from under you. He's hard on everyone.
knock the props out from under someone
Fig. to destroy someone's emotional, financial, or moral underpinnings; to destroy someone's confidence. When you told Sally that she was due to be fired, you really knocked the props out from under her.