Who's got the more viral meme on Iraq?   Let's begin with a brief except from John McCain's ferocious attack on Obama today:  

Though victory in Iraq is finally in sight, a great deal still depends on the decisions and good judgment of the next president. The hard-won gains of our troops hang in the balance. The lasting advantage of a peaceful and democratic ally in the heart of the Middle East could still be squandered by hasty withdrawal and arbitrary timelines. And this is one of many problems in the shifting positions of my opponent, Senator Obama.

Now consider part of Obama's response: 

The difference in this race is that John McCain is intent on spending $10 billion a month on an open-ended war, while Barack Obama thinks we should bring this war to a responsible end and invest in our pressing needs here at home.

Obama has a problem. He needs to do one of two things.  He's done neither so far.   Either he must directly and forcefully refute McCain's claim that "victory in Iraq is finally in sight" as some sort of fantasy.  Or he must  directly and forcefully  say why his approach is a better guarantor of victory. 
The phrase "a responsible end to the war in Iraq." which Obama (and CLinton when she was running) intones frequently is monumentally unclear in its intentions.   
Multiple Choice Question
A responsible end to the war in Iraq constitutes: (a) victory 
(b)  defeat
(c) neither victory nor defeat, but something else. 
If you answered (a), explain how Obama's recipe for ending the war is a better recipe for victory than Mcain's is.
If you answered  (b) resign yourself to probably a democratic loss this year.
If you answered (c) explain what that third thing, which is neither victory nor defeat is, say  how is that different from defeat and why is it acceptable.
I think Obama and the democrats generally counted on Iraq still being an utter mess come November, which would have meant there would be no explaining to do and no credible claim on behalf of the Republicans that "victory was in sight."   And that was a perfectly reasonable assumption at the time.  When the campaign got seriously underway,   Iraq was still looking nothing but an interminable Civil War that we could have no helpful role in. 
That was my view too. But it doesn't quite look that way now.
Unfortunately,   McCain is being very, very effective in hammering the theme that Obama isn't tough enough and isn't prepared enough to be Commander in Chief.  Obama has to decide and be firm in that decision and explain clearly what can or can't be achieved in Iraq, how we will achieve it, and why he is the best person to achieve it. "end the war responsibly" just won't do against McCain's constant and somewhat credible (but ultimately empty) claim that some sort of "victory" is in sight.   The challenge is to rebut that claim without seeming weak and defeatist. 
Or so it seems to me.