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.
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]
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.