Stanley Kurtz examines Chicago newspapers and Obama's articles during his tenure as a state senator and says:
What they [newspaper columns and articles] portray is a Barack Obama sharply at variance with the image of the post-racial, post-ideological, bipartisan, culture-war-shunning politician familiar from current media coverage and purveyed by the Obama campaign. As details of Obama's early political career emerge into the light, his associations with such radical figures as Reverend Jeremiah Wright, Father Michael Pfleger, Reverend James Meeks, Bill Ayers, and Bernardine Dohrn look less like peculiar instances of personal misjudgment and more like intentional political partnerships. At his core, in other words, the politician chronicled here is profoundly race-conscious, exceedingly liberal, free-spending even in the face of looming state budget deficits, and partisan. Elected president, this man would presumably shift the country sharply to the left on all the key issues of the day-culture-war issues included. It's no wonder Obama has passed over his Springfield years in relative silence.
Read the whole article for substantiation of this claim. It's a major piece of research which should serve as the touchstone for any future discussion of Obama's ideological core.