But the danger is more than our inability to fight another war.  There is the danger that we are breaking the Army and Marines.  Barry McCaffrey voiced these concerns in recent testimony before the U.S. Congress:

With US requirements in Afghanistan - estimated by McCaffrey at four brigades permanently engaged in a campaign that would last 15 years, a continued war on terrorism in Southwest Asia has become nearly impossible. Additionally, McCaffrey says, "The US Army is starting to unravel. Our recruiting campaign is bringing into the army thousands of new soldiers who should not be in uniform" - those with criminal records, who have used drugs, who have been given moral waivers, or who have not graduated from high school. A senior Pentagon official agrees. "We have increased our recruiting totals and tripled the number of our police battalions," he says, bitterly. "We will soon have to build new stockades to handle the influx."

And let's not forget the views of the Joint Chiefs of Staff:

In military parlance, Inman and Warner's call for a "cleaner command structure" is reflected by complaints of senior military officers that "the interagency process is broken" - code for the view among the staff of the Joint Chiefs that no one is listening to their views.

"The JCS has been thumping the table for two years over how we can't sustain our troops levels in Iraq and no one has been listening," a Defense Department official says. "No one is talking to anyone. During Rumsfeld's term you would have thought that we were at war with Condi Rice, not al-Qaeda."

And this is just the personnel.  We are not even beginning to address the need to re-equip Army Reserve and National Guard units with planes, trucks, armored personnel carriers, and Humvees.  Add to this the cost of taking care of the wounded--both physical and mental--streaming out of Iraq and Afghanistan.  The economic cost is enormous but is dwarfed by the human cost.  Tough to put dollar signs on broken hearts, shattered minds, and tears for the dead.

Come September I suspect John McCain will be backing away from his claim that we will spend 100 years in Iraq.  We won't  because we cannot afford the bill.