Obama is a centrist. Gingrich is a lobbyist and influence peddler who supports whoever writes the biggest checks. Romney is unable to hold any solid political views and apparently has no ambition (policy-wise that is) other than to become president... and then... who knows. The centrist case for Romney is that he'd be a competent technocrat that won't be prone to elementary school mistakes. That's more than you can say about the rest of the Republican field, but we already have a president in that mold in Obama.

Even a left-leaning voter like me who has plenty to be disappointed in Obama, has no alternative available in this race. Obama offers basic decency and attempts at competent management of the government which are insufficient responses in the face of America's various crises. All the Republicans have to offer is an even less helpful reactionary politics incapable of introspection or responsibility.