Why wasn't the opposition party oppositional enough? Where was the supervision? Why did Romney crumple mid-attack in the second debate? Where was the vigilance? Where was the vigor? Where was the outrage? The American people were deprived of a fair election, and the Republicans — who presumably wanted to get the President's hands off the machinery of power — didn't see what was being done or they didn't want to talk about it or — to voice the last and paranoid-sounding option — they were complicit.
Here's a list — to be lengthened — of things that might have happened:
1. The President's machinations were so devious and brilliant and that it was just too hard for the Republicans to uncover them in time to enlighten the voters.
2. The Republicans had good reason to believe that the American people resisted thinking ill of the famously likeable President and so they pursued campaign strategies that allowed people to maintain this treasured belief. Their idea was: He's a nice guy but it would be good to switch to this other person who's also nice and will do an even better job. That's lame, we can see in retrospect, but it was the decision at the time.
3. The Democrats' theme was the meanness of Republicans, and muckracking and mudslinging would have risked reinforcing that theme. It seemed like a better bet to stay clean, especially once the scrappier candidates — Gingrich and Santorum — lost out to the gentlemanly Romney.
4. Obama's prime target was the Tea Party (which had crushed him in the 2010 midterms), and the establishment Republicans were at odds with the Tea Party movement. I'm not saying I believe this, but sober reflection tells us we need to redraw the line between paranoia and vigilance. The theory is that establishment Republicans appreciated the suppression of the Tea Party.