The upper echelon of Republican Scott Brown’s Senate campaign in Massachusetts is filled with staffers who once worked in former Gov. Mitt Romney’s employ. But with the eyes of the nation on the state’s Jan. 19 special Senate election — and with other Republican luminaries such as Rudy Giuliani traipsing through Massachusetts for Brown in recent days — Romney himself has been conspicuously absent. Despite his status as one of the GOP’s most prominent national figures and a prospective 2012 presidential candidate, the former Massachusetts governor hasn’t appeared publicly with Brown since late October. Back then, when almost no one...