I don't care who you are or what your issue is, you don't shake your finger in the President of the United State's face. (Or any legitimately elected world leader, now that I think about it.) Remember when Bush was in the White House and the Republicans were very critical of anything they interpreted as disrespect, chiding the Democrats that "if you don't respect the man, you must still respect the office?" Well, it seems that only applies to Democrats apparently. I despise Bush, but if I had met him when he was still president I would have shaken his hand, called him "Mr. President," and been polite and respectful. That's just common courtesy and general standards of adult behavior.
I don't believe for a minute that Jan friggin' Brewer was unaware of the cameras. This was a staged, ambush photo-op. She wanted to get her picture out there scolding the President to score points with the conservative base. It's no different from that asshole who shouted "YOU LIE!" at President Obama during the SOTUS a while back. Instead of dismissing the disrespectful idiot as the buffoon he most certainly was, he was lauded by many Republicans for "telling it like it is" and "standing up to Obama." (Those of us who live in the adult world are aware of the fact that anytime anyone says they "tell it like it is," what they really mean is "I am a rude asshole who doesn't know the basic tenets of adult behavior.") Brewer is no different. She was deliberately rude and disrespectful of the President, and she did it in a time and place where she knew her little staged finger-wag would make the papers. But rather than be chided for her transparent, manipulative rudeness, she will be feted as some kind of conservative hero or something.
I know it would pretty much cost him the election....but it might almost have been worth it to see President Obama just bitch-slap that manipulative attention whore right there on the tarmac.