I'm not sure where this idea originated that Obama was some kind of pie-in-the-sky idealist and not a politician. Being a politician necessarily means making compromises, and this is not a bad thing. Sometimes one even has to make compromises on issues one really cares about and may even violate a principle or two. This is why pundits and politicians are different.
I do think Obama has ideals and principles and wants to accomplish grand things, but this makes him no different than most politicians.
The Republicans have been -- gasp! -- discovering that Obama is a politician. As in most ways lately, Republicans as a class have been pretty dumb and underestimated Obama all along. At the rate they are going they will underestimate him all the way to the White House.