What exactly are "Priviledges and Immunities"?

Factual Questions
1

A GQ that may degenerate into a debate so expect this to be moved to GD.

I was reading about what was happening with Arizona’s SB1070. I for one don’t know why AZ cannot ban illegal immigration because in my IANAL mind

[QUOTE=14th Amendment]
No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States.
[/QUOTE]

Which echoes what was written in the original Constitution. Combine that with the 10th Amendment (apparently declared unconstitutional by the case *Lincoln v Davis *(1865) ), it seems that Arizona can ban illegal immigrants because:

  1. “Priviledges and Immunities” doesn’t apply to aliens, legal or illegal.
  2. In regards to illegal immigrants, the Feds would be hard-pressed to say, “You’re not here legally, but we can’t stop you from traveling around.” Doesn’t stop the hypocracy however.
  3. Mexico hates it. OK, that’s not a legal reason but ever since Vincente Fox, Mexico has a tradition any president hating the US banning illegal immigration. Besides “WTF?!”, should I mention how the Mexican Army stops illegal immigration from Guatemaula? The official Mexican stance just rubs me the wrong way.

OK. GD aside, what exactly are the “Priviledges and Immunities”?
What did it mean in the original Constitution? What about when it was rewritten into the 14th Amendment?
Has the interpretation by the courts remained consistant? Has it morphed like “interstate commerce” or “eminent domain”? Is it ignored like the 10th Amendment or is it whatever that Judge/Justice wants it to be like the 9th?

2

The Privileges & Immunites clause of Article IV guarantees the fundamental right to travel between states and to take up residence in another state, subject to reasonable residency requirements. The P&I Clause of the 14th Amendment doesn’t mean much of anything anymore; it was made a “practical nullity” by the Slaughter-House Cases just a few years after the 14th Amendment has passed. Since then there has been practically no jurisprudence involving the 14th Amendment P&I Clause. The Equal Protection Clause gets all the action.

3

The contention is that Arizona cannot enact any laws concerning illegal immigrants because that field (illegal immigrants) has been preempted by the federal government (by law, not by the constitution). In addition, individual states cannot pass their own laws concerning illegal immigrants because the country needs a uniform policy in regard thereof.

However, it appears to me that Arizona’s law concerns only the method of identifying such individuals. It does not purport to amend any federal law nor change the federal law in any way.

BTW, it’s * privileges* and consistent.

4

They are things that, thanks to the Supreme Court, do not exist (per above in the Slaughter-House cases). The Court has shown no interest in revisiting that particular part of the 14th Amendment, with the notable exception of Clarence Thomas and his opinion in the recent McDonald case.

It’s a dead issue, though it shouldn’t be.