Second Amendment is Essential Act of 2021 This bill directs the Department of Homeland Security to designate the business of importing, manufacturing, or dealing firearms, or importing or manufacturing ammunition, as a critical infrastructure sector. Additionally, the bill states that individuals who are employed by those entities are critical infrastructure workers. The term critical infrastructure means systems and assets, physical or virtual, so vital to the United States that the incapacity or destruction of such systems and assets would have a debilitating impact on security, national economic security, national public health and safety, or any combination of those matters.