Determined not to let a recent slate of attacks on Mitt Romney’s financial and job history slide quietly into the weekend, Democrats stepped up their attacks on Friday, again criticizing Romney for his failure to release his tax returns. Releasing the returns, Democrats say, would help evaluate the legitimacy of a Boston Globe story published Thursday that said Romney remained involved in managing Bain Capital after he left in 1999, a tidbit reporters got from SEC documents showing him as chairman in 2002.