cut the ground from under
cut the ground from under {v. phr.} {informal}
To make (someone) fail; upset the plans of; spoil the argument for (a person) in advance.
Paul wanted to he captain but we cut the ground from under him by saying that Henry was the best player on the team.
Several workers applied for the retiring foreman's job, but the owner cut the ground from under them by hiring a foreman from another company.
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Source: A Dictionary of American Idioms