cut the ground from under (someone)

cut the ground from under (someone)

To suddenly cause problems for someone. I plan to cut the ground from under the prosecutor with this line of questioning.
See also: cut, ground
Farlex Dictionary of Idioms.

cut the ground from under

Unexpectedly withdraw support or destroy one's foundation, trip someone up. For example, Overriding his veto, Congress cut the ground from under the President. This metaphoric phrase alludes to removing the solid earth from under someone. [Mid-1800s]
See also: cut, ground
The American Heritage® Dictionary of Idioms by Christine Ammer.

cut the ground from under someone

or

cut the ground from under someone's feet

If you cut the ground from under someone or cut the ground from under their feet, you make their ideas or opinions seem less impressive, often by doing something unexpected. The sudden announcement was seen by many as an attempt to cut the ground from under the president's feet.
See also: cut, ground, someone
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • cut the ground from under
  • cut the ground out from under
  • cut the ground out from under (one)
  • cut the ground from under someone
  • cut the ground from under someone's feet
  • cut the ground from under(neath) (one's) feet
  • underneath
  • cut the ground from under somebody/somebody's feet
  • cut eyes at
  • cut eyes at (someone or something)