Why exactly is there this double standard in politics?

I remember after the Tucson shooting, Obama started calling for an 'age of civility' and 'toning down all the language.' Since then, Republicans have been compared to Hitler, Democratic congressmen declare on the floor that Republicans want to kill old people and minorities, those 'evil cross hairs Palin put over congressmen' have re-appeared over Republican governors, democrats have said Clarence Thomas should by lynched, Chris Matthews stated that Republicans want to destroy the country, and on and on, and oddly, Obama hasn't uttered one word on all that 'civility' he was talking about a few months ago. Then there's Obama's gaffes, which, when Bush, Bachman, or Palin made similar, were headline news, whereas you'd be lucky to even hear a mention about Obama's (Corpsmen being refered to as 'corpsemen' multiple times, saying the US was founded 20 centuries ago, visiting 57 states...all Bush had to do was say 'nuclear' wrong and people went crazy.) This list can go on and on.....so, what gives?