knock the bottom out of

Also, knock the props out from under. Render invalid, undermine. For example, The discovery of another planet that might support life knocks the bottom out of many theories, or Jane's skilled debating knocked the props out from under her opponent. The first expression dates from the late 1800s, the variant from the first half of the 1900s.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.