Some argue technicalities - sometimes important but most often trivial and meaningless and merely opportunities to avoid the truth. Others argue principles - always important and superior to technicalities.
It is clear, in this case, that "reasonable suspicions" leads to "probable cause" it shouldn't be of any concern. This is an established law enforcement principle - not something invented by Arizona to circumvent the Constitution as some suggest. It is also clear that Arizona's law only permits law enforcement to handover to the federal government someone they reasonably suspect to be an illegal alien and that they encounter in the course of their routine law enforcement work. The criteria is essentially no different than that used by federal law enforcement officers to determine reasonable suspicions or probable cause! There's nothing wrong with that "principle" and, for that matter, neither the "technicalities".
Even the DOJ's stupid lawsuit doesn't clearly claim a violation of the 4th amendment. Most of it just makes excuses for the federal government's selective non-enforcement of immigration law and implies that Arizona is somehow in violation of federal supremacy, preempting federal law, and, just to throw in the kitchen sink, restricting interstate commerce. All of these are false claims!
It's a shameful act by the Obama administration that seeks to gain favor with the supporters of illegal immigration. It has nothing at all to do with the 4th amendment. If it did, you can bet that would be the main stanzas of the DOJ's whining 25 page song.