Cutting through the unproductive sarcasm and pissing contests and referring back to the original poster, the tea party activists (and anyone else who opposes the law) will still be able to denounce the actions of the federal government with, at least, internal consistency. This is because "legal" does not necessarily equal "right."
The supremacy clause is a legal technicality. Important and, at times, useful, but a technicality nonetheless. If the Arizona law is struck down by the supremacy clause, the fact still stands that a state, with the support of a majority of Americans, wants to stem the flow of illegal immigrants across its border with Mexico, and it does not believe that the federal government is sufficiently enforcing federal law. If the Arizona law is ruled to be unconstitutional because of the supremacy clause, that ruling will say nothing and mean nothing as regards the federal government's failure to address the concerns of American citizens. If anything, it would actually seem to strengthen the argument that the federal government is not listening to its citizens' concerns (unless they struck down the Arizona law for procedure's sake, and immediately stepped up their own enforcement).
As far as Obama's credentials are concerned, yes, he is an expert on constitutional law, as evidenced by his tenure at Harvard (as a side note, the fact that he was a teacher says nothing good or bad, by itself, of his competence in any capacity). But that does not mean it's "his game" or that he is infallible. Constitutional law is an incredibly vague, unpredictable field of the law, precisely because it ultimately falls to the Supreme Court of the United States to define what is, and what is not, "constitutional." And their opinions on the matter often change drastically.
And kudos to texmaster for posting some truly useful information. Interesting stuff, there. And I'll be very interested to see how that case pans out. The supremacy clause only prevents states from passing laws that conflict with federal laws or undermine some purpose of the federal legislature. I'll be interested to see exactly what law or purpose the Arizona law supposedly conflicts with or undermines (I haven't read any of the government's briefs and I don't know if they've been released yet).
Cheers,
The Black Sheep