As a fellow debate watcher said last night, Obama is an "organized thinker" — his small points inevitably lead to large conclusions. (For instance, in the debate last night he noted that the United States consumes 25% of the world’s annual oil production, but only has 3% of the world’s oil reserves. This means that offshore drilling will not solve our energy problems — no matter how many times Republicans call for more drilling.)
As a thinker, McCain is as much a loose cannon as he is a maverick. This explains why he’s good in a town hall format, where he can jump from one point to another, but not so good in speeches, where the speaker needs to build a platform on which to stand and make his logic clear.
This difference leads to frustration for McCain in debates. You saw it against Romney, and we saw it last night against Obama. As he clenches his jaw and glares, you can see him wanting to devastate the younger man, but his shots (such as the jibe about bear DNA research) go wild as often as not. Obama ignored most of them, simply correcting the outright lies (such as McCain’s complaint that Obama would raise taxes on families making $42,000 a year). This only makes McCain madder.
As Larison points out at The American Conservative:
Obama as having done better than McCain. The CW [conventional wisdom] has now been firmly
entrenched. The telling thing is that this has happened in a debate
for which a lot of us assumed McCain wasn’t very well-prepared (he was
grandstanding in D.C.saving the world, after
all) and focused on a subject where McCain is supposedly some grand
master and Obama is allegedly a novice. Obama proved that the idea
that he is somehow not well-versed on foreign policy is nonsense. From
here on out, McCain is in a lot of trouble. In future debates he can’t
just keep saying, “Earmark reform, drill, baby, drill, maverick” and
expect people to pay attention to what he says.