Firstly the 2000 election is largely believed by many Americans to have been stolen by Bush (read Jeb Bush in Florida). Also, after 9/11, in 2002 bush had 84% support by Americans, I bet much of the leftwing was part of it too.
But after 2003, he's been a royal fuckup. No one can deny that. Iraq war - no WMD costing over a trillion now (more than the bailout) and then costing more lives. Even THEN, some in the left and many in the centre-left/middle did support him as lesser of two evils against Kerry. But then Katrina came and he was exposed. Then the economic crisis and him not knowing a thing about what the heck to do. Hence, the Republicans lost in both 2006 and 2008 in house and senate seats.
I bet you conservatives love the fact that Bush introduced the most socialist plan in American history - the $800 Billion bailout. That goes against every conservative principle in history. Yet you go rant against a guy who's just in. This is the idiocy of the ultra-right wing. They think they are going against the grain and being heroic in the process but know very will that when they express that idea in the mainstream audience, they will not be able to defend it. So they talk and vent in forums.
This is exactly what Limbaugh makes money from, that 14% of the base that cannot accept the fact that a black man became the President.
To someone who said the right-wing base is 50%... I cannot help but laugh the Registered Republican base is about 28% while democrats are around 39%-45% in the recent election last I checked. If you say many have centre-right views I'll agree but to say that they are rightwingers is far from the truth.
Republicans need the support from the middle and some democrats, and if people like Limbaugh and those who share his views keep pushing things without giving Obama a chance, they will not win for a long time and lose their rising stars like Bobby Jindal and Eric Cantor and end up with more old rich white guys like McCain and Romney or Pastors like Huckabee who will keep losing.