It wasn’t any “one thing”.
This is more a case of multiple issues.
1) Obama has NEVER been a good platform debater. He usually comes off dry and “professorial”, so that was nothing new. And the right’s base has always viewed advanced education as being “elitist” when it comes to Obama. It almost feels like a left-handed racial rebuke. Like a black-man with an education is trying too hard or pretending to be something he’s not. This is not to imply that all on the right feel this but there are enough that it gave the “Elitist” taint traction.
2) Obama has a full time job as PRESIDENT that keeps him pretty occupied. The morning briefings he gets 7 days a week aren’t exactly “brief”. They typically come in a binder of 30 to 50 pages, in synopsis. That’s like having school every day and having to answer the quiz that afternoon.
3) The Romney we’ve seen for the last 3 or 4 months wasn’t the Romney that showed up. This “Denver Romney” was more akin to the Liar character (Jon Lovitz) from Saturday Night Live so Obama had one set of debate points and Romney invented a whole list of fantasy points with no basis in reality. Even going so far as denying months of printed, spoken and web-present positions HE took during the primaries and up to the day before Denver (His people spent the next day rolling back half a dozen statements like “I won’t kill the pre-existing conditions rule in Obamacare”). This was designed specifically for the purpose of throwing Obama’s responses out the window.
4) Maybe altitude adjustment had him off a bit it wasn’t just that and definitely not “mostly” that.
The truth is Romney’s people KNOW he’s got a “flip-flopper” veneer and they’re used to having to roll his crap back. It’s gotten so expected it has become background noise. This was a calculated plan to make President Obama look weak, unprepared, off his game, whatever. In the end, almost everything Romney said was shown as lies, inaccuracies and bullet-points with no possible basis in real economics but to the red-meat-right, it doesn’t matter. They will back him regardless because he is all they have. Between the rabid Tea-Party and the death of the moderate Republican, they could put up an animatronic puppet from Disney and they’d back it.
Obama suffers from one major flaw for many of us on the liberal left; he’s too polite. When Romney lied, he should have said “That, Sir, is a bald-faced lie and you know it”. Instead President Obama stood back for fear or apprehension in being labeled the “Angry Black Man” or that “Uppity N-word” because we all know that there is a huge breath being held on the extreme right in the hope that he does get angry they CAN use that label. We are not a post-racial society, as incidents daily show.
Obama has a bigger mountain to climb for a hundred reasons and he has to climb it carrying the weight of a struggling economy the Republican party had an eight year hand in creating and has spent the last 46 months trying to keep under water so they would have a platform for this election. Mitch McConnell made that much clear and John Boehner has strived to enforce the plan of forced stagnation through congressional malfeasance.
Did Obama take it on the chin in the debate? Yes. Was it fatal? Hardly. Does it make his campaign a little harder? Sure. But in the end, Romney gave the Obama reelection campaign enough advertising material to last a lifetime.