One way to look at the wars in Iraq and Afghanistan is to see them as one war with two fronts.  Germany fought two-front wars twice in the 20th century, and it was almost able to prevail because it had the advantage of interior lines.  The German Army could quickly shift divisions and corps from the Eastern to the Western front or vice versa, using the superb German rail system.  Unfortunately, the U.S. lacks the advantage of interior lines in its ongoing two-front war.  No railways run from Baghdad to Kabul.

U.S. commanders in Afghanistan have reportedly requested an additional 10,000 troops.  Secretary of Defense Robert Gates was recently quoted in The Washington Post as telling the Senate Armed Services Committee, "I believe we will be able to meet that commanders' requirement, but in the spring and summer of 2009…we do not have the forces to send three additional brigades to Afghanistan at this point."

The only source for additional troops for Afghanistan is Iraq.  The September 2008 issue of Army magazine quotes Joint Chiefs Chairman Admiral Michael Mullen as saying, "I don't have troops I can reach for, brigades I can reach, to send into Afghanistan until I have a reduced requirement in Iraq." 

Without railways running on interior lines, we cannot move three brigades from Iraq to Afghanistan this week, then move them back to Iraq again a few weeks later if the situation there demands them. That means any shift of forces requires long-term stability in Iraq.  Neo-con voices in Washington are now claiming "victory" in Iraq, which, if it were true, would release American forces stationed there for redeployment.  This appears to be what Secretary Gates is counting on when he says we should be able to meet commanders' request for 10,000 more troops in Afghanistan next spring or summer.

But I fear this represents a falsely optimistic reading of the situation in Iraq.  In my view, the current relative quiet in Iraq is merely a pause as the parties there regroup and reorient for the next phase of the war.  Unless we have the good sense to get out of Iraq now, while the going is good, we will be stuck there when that next phase starts.  We will not then be in a position to shift forces from Iraq to Afghanistan, because without interior lines, any such shift much be long-term.
While most of the stuff on the internet is junk, the junk pile does hold an occasional diamond.  One such is a daily report called "NightWatch," written by a retired DIA analyst, John McCreary.  As quoted in The Washington Post's "Tom Rick's Inbox," "NightWatch" for September 11, 2008 said:

The U.S., as the most powerful faction (in Iraq), imposed power sharing on the Kurds, the Arab Sunnis and the Arab Shiites…Power sharing is deceptive because it always features reduced violence.  It looks like victory, but is not….

Power sharing can last a long time, but it is not a permanent condition and does not signify one faction's triumph over the others.  It is never an end state, but rather a transitional period during which the participants prepare for the next phase of the struggle….

Thus, power sharing is always a prelude to violence.

If the next phase of Iraq's civil war breaks out before spring 2009, Secretary Gates's promise of more troops for Afghanistan will go unfulfilled.  Both the Army's and the Marine Corps' cupboards are bare.  We will in effect face enemy offensives on both fronts simultaneously, with no reserves.

Even with the advantages of interior lines and excellent railways connecting both fronts, Germany was not able to deal with such a situation from the summer of 1944 onward.  Lacking those advantages, our predicament will be worse.  We will find ourselves face-to-face with failure both in Iraq and Afghanistan, with few if any options.  If an attack on Iran has meanwhile brought that country into the war against us, we will face a third front.  Events in Pakistan could create a fourth.  It is the nature of long wars that they tend to spread.

Whoever the next President is, he is likely to find himself living in interesting times.