Border Defense or Invasion Springboard: Why is Poland Massing Troops on Frontier With Belarus?

Poland kicked off a large-scale military operation along the border with Belarus on August 1, ostensibly to secure the frontier in the face of what Defense Minister Wladyslaw Kosiniak-Kamysz characterized as a migrant-fueled “hybrid war” against Warsaw. Why does Minsk have reason to be wary of Warsaw's official justifications?