Among the criticisms I have heard that I would judge to be invalid are not so much rants, but just tired far-right talking points: the bigoted innuendo concerning suspicion about his birth nation, his race, connection to socialism and/or supposedly radical fiscal policy.
He's a middle of the road, conservative "Blue-Dog" Democrat for heaven's sake. Nothing about his administration has been particularly daring or remarkable....and THAT will most likely be his problem in 2012, not the kooky stuff.