poke a hole in (something)

Translations
проделывать дыру в (чем-то)
She tried to poke a hole in his argument, but he had a strong defense.
Она пыталась проделать дыру в его аргументах, но у него была сильная защита.
Definitions
To find flaws, weaknesses, or errors in an argument, plan, or idea; to criticize or challenge something by pointing out its problems.