IMPEACH BUSH

(CNN) -- Army Sgt. Chris Tucker is a textbook case of the wear and tear of multiple deployments to Iraq and the strain this remarkably frustrating war has been on the men and women who serve in it.

Tucker was a young specialist when his tank company rolled into Baghdad shortly after the war started in March 2003. Only 24 years old, he was readying for his third deployment when we visited him recently at Fort Stewart, Georgia.

Tucker walks in pain and says both feet need surgery. He was recently fitted for a hearing aid -- one toll of being exposed to many explosions.

He also has been on medications for sleep disorders and depression that started after his first deployment four years ago. His wife, Nicky, worries the nightmares and sleepwalking will continue in Iraq when she is not around to keep watch.

"From when he first went in and now -- he is not the same," Nicky Tucker tells us. "He's always trying to be the bigger man and take care of himself but there's a point where he has to be looked at and he needs to be taken care of, but the mission always comes first and he has to worry about himself later."

Or as Chris Tucker puts it: "I'm kind of banged up but I think there are many other people in the same position as me. ... You would hope that they would take care of you better, but, umm, some things are out of your hands."

Tucker also is an example of a trend many in Congress and the military say leaves troops at greater risk in Iraq and contributes to long-term readiness and training issues. His unit trained for months in their tanks, but at the last minute, the unit was re-tasked to ride Humvee patrols, Tucker says.

He has a compatriot in Staff Sgt. David Bess, who is stationed in Balad, Iraq.

Bess is an infantryman who prefers to be on his feet, but spends four or five nights a week in the passenger seat of a Humvee. Bess, in sports jargon, is playing out of position -- an increasingly common dynamic as the Army scrambles to fill roles in Iraq.

"It is not necessarily my preferred mission," Bess says. "But it is an important mission, and I want do to the best I can."

He leads convoy security missions in one of Iraq's most dangerous areas; we ride along one night on a trip from Balad to Baquba, swerving to avoid trash piles and potholes that could be hiding roadside bombs.

During the mission, his eyes dart nervously as he scans the dark roads for any sign of danger.

Before each convoy run, he assembles his men for a few moments of silent prayer. He asks for blessings for his patrol.

"And then I always say a blessing for my wife and kids at home," he says.

Like Bess and Tucker, 27-year-old Stephen Castner's unit was re-tasked. Although he was an electronics and communications specialist, Castner's National Guard unit was initially designated as an artillery regiment. The entire battalion was re-assigned to combat infantry before deploying to Iraq. In June 2006, on his first mission in Iraq, Castner died from wounds he suffered when his Humvee was hit by a roadside bomb.

"I think this was a classic example of using National Guard troops who were not prepared in any sense," Castner's father tells us from his home in Wisconsin.

The military says Stephen Castner's death was a part of war.

"There is nothing we didn't give him in equipment and training that would have prevented the loss of Stephen Castner. I mean we have scoured that very hard," Lt. Gen. Steven Blum tells us.

Blum does say that the retasking and the scramble to upgrade equipment in Iraq could be interpreted as a breach of war doctrine.

"No question. And the lesson is a fundamental one of all prudent military planners," Blum tells CNN. "You plan for the worst case. You hope for the best, but you plan for the worst."

Price of war

Four years into the war, the costs in lives and money are dear.

The human toll: More than 3,500 Americans have died in Iraq; more than 25,000 have been wounded.

The financial cost: $500 billion in spending, at a rate now of more than $2 billion a week.

There is another price: More than two-thirds of active duty Army brigades are rated not ready for their mission because of manpower or equipment shortages, most of which can be directly attributed to Iraq. It is a readiness domino effect.

The numbers for the National Guard are even more alarming: Nearly 90 percent of Guard units not in Iraq are rated not ready for missions.

"Right now the United States does not have any depth of strategic reserve in our ground forces," military analyst Michelle Flournoy says. "Meaning we don't have ground forces ready and willing to deter a conflict or keep a small problem small."

A Democratic senator says the military was unprepared for a protracted campaign.

"It all traces back to a lack of a coherent plan when they went in -- understanding that this might evolve into an insurgency," Sen. Jack Reed of Rhode Island says. Reed, a Vietnam era veteran of the Army's 82nd Airborne Division, recalls a trip to Iraq in summer 2003 and the number one complaint from frontline troops: A lack of armored vehicles.

When he came home, the military acknowledged it needed more, but resisted when Reed and other members of Congress sought more money than the Pentagon said was needed.

"I think they were still in the stages of denial," Reed said. "Saying, 'Well this is not necessary. Why do we want to invest in these armored Humvees. Because frankly we won't be needing them if we leave Iraq in the next several months."

Four years later, U.S. troop levels are in the 170,000 range. And explosions -- from homemade bombs -- are, according to Army data, responsible for more than six in 10 of the deaths and more than six in 10 of the major injuries in Iraq.

Those injuries, and the countless exposures to explosions that do not result in noticeable wounds, have military commanders increasingly worried that brain injuries could be the Agent Orange of this war -- the toll hidden until long after the troops return home.

Maj. Gen. Dennis Hardy, the deputy commanding general of ground forces in Iraq and Afghanistan, tells us during a visit to his office in Kuwait that he worries about the future toll of brain injuries.

"We probably have to do a more formal tracking process," he says. "To know who has been in the vicinity of explosions, monitoring behavior to see if there's any change or indicators."