Because, as Byron York notes, he is:
There are lots of reasons Republicans oppose Obama’s initiatives. But the issue of executive competence alone would be reason enough to oppose; why should GOP lawmakers entrust far-reaching new authority to a president who is struggling to run the executive branch as it is?
Honestly, at this point the incompetence is almost an endearing thing about the President. At least he can’t actually do anything to harm the country that’d be remotely as bad as the stuff that he and the Democrats did in 2009 and 2010. Not much of a balm, I know, but I didn’t cause this situation.
— Rick Wilson (@TheRickWilson) May 27, 2014
PS: I also didn’t vote for the guy in 2012. Mind you, I didn’t vote for Barack Obama in 2008, either, but people can plausibly say that they hadn’t realized just how badly their 2008 vote would turn out. Harder to do that with the 2012 vote.