Fourth Ammendment: "Reasonable suspicion" in AZ law not a reasonable search, despite the fact that it uses the word reasonable. Suspicion is not enough. The courts have clearly found that the probable cause needed for a reasonable search is "a reasonable amount of suspicion, supported by circumstances sufficiently strong to justify a prudent and cautious person's belief that certain facts are probably true." It sounds the same if you stop after the first 5 words, but the AZ law ignores the rest.
Article 4, section 3, clause 2 directly gives the Federal government the power to "make all needful Rules and Regulations respecting the Territory".
Fourteenth Ammendment:
Searching citizens who are suspected of being illegal and requiring them to affirmatively prove their citizenship violates the Fourteenth Ammendment, section 1:
"No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States."
It goes on to guarantee due process and equal protection
due process - The process of requiring people to prove their citizenship with papers at the whim of the police is not due process. There is a lot of case law defining what due process is, and this ain't it.
Equal protection - requiring Hispanics to display documents proving their citizenship would clearly violate equal protection. Case law is clear. As many laws do that have been struck down, this law does not use the word Hispanic, but the "probable effect" is that people who look Hispanic will be confronted by police a lot more.
And that gets to the fundamental of what it means to be American. I am all for confronting criminals, but it is wrong to search and detain people who you might think look like they are the criminal type, even if some turn out to be criminals. Others feel that catching criminals means giving up our rights because they know that it isn't white people who are giving up their rights, and because we don't like "their kind" and don't really care that some are criminals, but some are not.