The former speaker of the House of Representatives, Newt Gingrich, is planning to formally launch on Thursday his bid for the Republican nomination to take on Barack Obama next year, the first of the candidates to do so.It has been a slow start this year compared with the same period in recent election cycles. Sarah Palin, the former Massachusetts governor Mitt Romney and other potential Republican candidates are holding back. The announcement by Gingrich, trailed by ABC News, might lead other candidates to join the fray.