Some American grocery stores already tested the waters by posting armed guards in its stores. This article is a few years old, but the precedent stands.
retailwire.com/…/hy-vee-creates-its-own-armed-sec…

Hy-Vee last week announced the introduction of an in-house armed security team to manage theft and in-store disturbances.

The Midwest grocery chain said in a statement that it has long worked with third-party contractors or off-duty law enforcement that work in a security capacity. The goal of bringing it in-house is “to create a consistent look for the security team and consistent approach to customer service and security across all [its] stores.”