And Jefferson used “Separation on Church and State” in a letter to the Danbury Baptists. That wasn’t in the Constitution, either.
What does that have to do with the EXPLICIT responsibility of the Federal Government to protect against invasion?
First, it isn't an 'invasion', it's a migration. An invasion would be a foreign military attacking on American soil.
Secondly, the Constitution does not give the feds the ability to arbitrarily patrol the borders, only to establish ports of entry for the purpose of collecting taxes.
The first part of this clause:
The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion;
simply prevents the feds from favoring one State over another should there be an attack on American soil.
The possibility of an undue partiality in the federal government in affording it's protection to one part of the union in preference to another, which may be invaded at the same time, seems to be provided against, by that part of this clause which guarantees such protection to each of them. So that every state which may be invaded must be protected by the united force of the confederacy.
St. George Tucker, Blackstone's Commentaries
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Conservatives constantly complain about overweening federal power, yet they cling to this clause as if it suddenly bestowed a carte blanche power on the feds....it does not.
The general rule was that the States were to protect themselves and call for federal assistance only if needed.
Giving the feds authority over denizens that reside in the States is not only unconstitutional, but suicidal as well.
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Again, Cain is right.
The only way to properly deal with unwanted visitors is to let the States decide if they want them there, and if not, to toss them out.