Byron York in the Washington Examiner compares Rubio to the GOP's best-known flip-flopper, Mitt Romney:

...Any reasonable reading of Rubio's positions then and now leads to the conclusion that he has executed a flip-flop of Romneyesque proportions. Rubio's flip-flop is even worse politically. While Romney switched to a position that was popular with the Republican base, Rubio has done just the opposite.
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Rubio's rapid evolution has baffled some of the people who rallied to his support in 2010. "He came across as the genuine article who believed things to his core, a passionate, from-the-heart principled conservative who spoke with conviction," says one Republican who helped promote Rubio's Senate candidacy when few establishment GOP figures supported him. "And immigration was not a small issue. It was so front and center in the 2010 campaign that it does create a certain level of distrust on other issues."...
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http://www.tampabay.com/blogs/the-buzz-f...-romney/2128482

The conservatives in Florida are probably more disappointed than the rest of us. Most of their newspapers have columns on Rubio's actions.