You don't get it both ways

It can be successfully argued that the federal government has defaulted on its responsibility to protect the states against foreign invasion. As a result at least one state, Arizona with more to come, have decided that self protection in the form of state laws pertaining to how to handle illegal aliens is required. Then comes the next step.

The federal government is considering a lawsuit to prevent the states from protecting themselves against the very thing the federal government has failed to do.

You don't get it both ways.

The federal government cannot fail to do its job and at the same time prevent the states from protecting themselves from federal government failure. The right to self protection cannot be usurped by the federal government. This is particularly true since the the only authority the constitution gives to the federal government is to set a uniform set of rules regarding naturalization of aliens who are "legally" in the United States (Aticle 1, Section 8).

Since all powers not specifically given to the federal governemnt are reserved to the states, or the people, the federal government has no authority to prevent a state from protecting itself from illegal foreign invasion.

Eric Holder, go pound sand.