Christopher Hitchens pretty much demolishes the idea that the Iraq war has "distracted" from the war in Afghanistan. AS the author points out, several of the Al-Qaida leaders in Iraq, most notably al-Zarqawi, arrived in Iraq after being driven from Afghanistan by coalition forces. Also of note is that the coalition forces in Afghanistan are comprised of many nations, including a number of NATO allies. He points out that the issues in Afghanistan are not from a lack of tropps and/or resources being applied there, the issue is that there is a 'safe haven' across the border where the Taliban are able to reorganize and plan their attacks - from Pakistan. Additionally, the counter insurgency lessons learned in the sands of Iraq are being utilized now in Afghanistan with some degree of success.
"In other words, any attempt to play off the two wars against each other is little more than a small-minded and zero-sum exercise. And consider the implications. Most people appear now to believe that it is quite wrong to mention Saddam Hussein even in the same breath as either a) weapons of mass destruction or b) state-sponsored terrorism. I happen to disagree, but just for an experiment, let us imagine that some regime did exist or did arise that posed such a combination of threats. (Actually, so feverish is my imagination that I can even think of one whose name also begins with I.) Would we be bound to say, in public and in advance, that the Western alliance couldn't get around to confronting such a threat until it had Afghanistan well under control? This would be rather like the equivalent fallacy that nothing can be done in the region until there is a settlement of the Israel-Palestine dispute. Not only does this mean that every rogue in the region can reset his timeline until one of the world's oldest and most intractable quarrels is settled, it also means that every rogue has an incentive to make certain that no such settlement can ever occur. (Which is, of course, why Saddam threw, and now the Iranians throw, their support to the suicide-murderers.)"
The very idea that the United States of today, the wealthiest and most powerful nation on the planet, should have a problem fighting a rather small group of religious fantatics in two relatively distant regions of the world simultaneously is patently absurd. The scale of the combat and the logistical complexities aside, our efforts today are minscule in comparison to the challenges the nation faced sixty plus years ago during World War Two - where we fought two significant nation states across two oceans half a world apart and over three continents.