Answer:
The members of Congress exercise a dual representation, being representatives of the states before the federal government, but also members of the federal government as they pass laws that concern the United States in general. Consequently, they can often have conflicts of interest when trying to resolve a certain issue, since the interests of the states are not always consistent with those of the federal government, and vice versa.
Therefore, it is the task of the congressmen to seek a balance between both sectors: seek to reach agreements or solutions that benefit as much as possible both the federal government and the states. For this it is necessary that they adopt a series of criteria that allow determining in which situations a criterion is more important at the national level, and in which situations the local criteria are more determining.
Therefore, the national interest should prevail in cases in which national security or government finances are compromised: in cases of defense, trade or energy, the national criterion should be the main one, since they are matters that directly affect the interests of the nation.
On the other hand, other situations require a criterion tending to favor the states: for example, in case of promoting immigration, the states have different social and cultural realities that would make immigration necessary or not, which would be impossible apply a single criterion at the national level.
