Wait, your counterpoint is that Obama is NOT "towards the center"? There is far more room to Obama's left than there was to McCain or Romney's right, at least in what they said during their primaries, and positions they purported to support.
I think the median Democratic politician is far closer to the 'center' of current American politics (and the center of the American electorate) than the median Republican politician. There's a lot of reasons for that, primarily since far more moderate Republicans have been replaced (in 2010 and 2014 in particular) than Democrats.
I think anyone who believes Obama is 'left-wing' is off base; he's certainly on 'the left', but by no means is he in the far left wing of American politics. He's a pragmatic Democrat, and while I believe he's further left of, say, Hillary Clinton, he's certainly not as far left as Elizabeth Warren or Bernie Sanders.