That is how "many" Democrats feel in Arizona. Betrayal is an emotion so visceral because it is so personal. When you think you know a person, especially when the person seems so much like you, and you support them and identify with them and then they become unrecognizable in a new position...you feel betrayed.
I have written the following many times. I loved Barack Obama, still love him, will always love him. I knew the guy, in the sense used here. I know people, one in particular, like him. Obama and I are close in age; both lawyers, I knew what that guy was thinking. Lawyers think in a certain way. Everything that Obama did and didn't do I either agreed with or I could understand how he could have done or not done it because I could have done or not done it. Lawyers have to make decisions. You don't have the luxury of endless study, as an academic does, for example. You have to make a decision. This is the case. You do your research, making sure you're thorough, get feedback from colleagues, whatever. Now it comes time to try the damn case. You have to decide. I knew Obama was never going to "do stupid shit." I knew it. And he never did. Never had a mind meld with a president like I had with Obama.