His face darkens. This Taliban tactic of lacing the countryside with explosives, he says, is "a more cowardly way to fight."
He and other Marine commanders say they understand why the Taliban uses the devices: Killing and maiming U.S. troops as they surge into Taliban strongholds let retreating insurgents live to fight another day.
"It creates survivability" for the Taliban, says Barnhart, operations officer for the 1st Battalion, 2nd Marine Regiment, fighting in this hilly northern district of Helmand province.
The surge of 30,000 servicemembers ordered by President Obama — bringing the total U.S. presence here to 100,000 — is in place and moving into areas where the Taliban has operated freely for years, the Pentagon says.
On Sunday, the International Security Assistance Force (ISAF), which oversees military operations in Afghanistan, said an "important phase" of the surge began this weekend in areas where the Taliban is strong in numbers.
Dubbed Operation Dragon Strike, it is an aggressive push in the southern part of the country where the Taliban awaits.
"We expect hard fighting," said Brig. Gen. Josef Blotz, ISAF's spokesman.
Coalition commanders fighting here for months say they have been pushing Islamist fighters out of village safe havens, but the toll on troops is high.
U.S. soldiers and Marines fighting in the provinces of Helmand and Kandahar — traditional strongholds of the Taliban — encounter numerous IEDs, or improvised explosive devices.
Troops injured seriously by the mines arrive daily at a NATO hospital at Kandahar Air Base.
In Helmand province, the 1st Battalion, 2nd Marine Regiment led by Marine Lt. Col. Michael Manning had been hit by 240 bombs (an average of more than one a day) and disarmed an additional 331 during a six-month tour that ended this month.
Manning and Brig. Gen. Joseph Osterman, who commands all Marine ground combat forces in Helmand province, say the increase in IEDs is proof the military's surge is working.
"The more you disrupt, the more he tries to find ways to disrupt what you're doing," Manning said.
Taliban fighters have suffered significant casualties when they battled coalition troops, Manning and Osterman say.
When that happens, the Taliban tends to fall back and seed fields, roads and orchards with IEDs during the night.
Such minefields are a last-ditch effort to hold off defeat, they say.
"The enemy would be glad to box us off and put an IED belt, essentially an area minefield, all the way around us," says Osterman, adding that Marines will not let that happen.
"We're constantly pressing the envelope, we're always pushing the (Taliban) farther out," he says.
Obama campaigned on a promise to ratchet up the war in Afghanistan, which he called the center of the U.S. fight against al-Qaeda and the Islamic extremists who attacked the United States on Sept. 11, 2001. As a U.S. senator, Obama opposed the troop surge in Iraq backed by President Bush. Now he is turning to a similar strategy to win in Afghanistan.
Additional troops have been deploying in stages for months and are in place, according to Defense Secretary Robert Gates. Gates said last week that the U.S.-led coalition has the resources "to partner with the Afghans and have some prospect of dealing with a resurgent Taliban."
Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, said it's too soon to tell how things will go.
"I do not in any way underestimate the degree of difficulty or the challenge," he said.
Helmand province in southwest Afghanistan has long been a haven for the Taliban, the clerical movement that imposed harsh Islamic rule until its ouster by the U.S.-led invasion in 2001.
In February, Marines pushed the Taliban out of the Helmand city of Marjah and are advancing farther into jihadist sanctuaries. As the Marines move from village to village, a pattern of combat has emerged.
Insurgents initially engage in hours of firefights with Marines over a period of days or weeks, Manning says. After suffering losses, they turn to a "cat and mouse" tactic of firing on patrols from concealed spots for several seconds, then fleeing.
"They got to get fairly close to do direct fire. When they do that, we kill them," Manning says.
Manning says radio intercepts of Taliban communication show the enemy force takes too many "significant casualties" from the engagements.
Unable to prevail in man-to-man combat, the insurgents turn to the mines, commanders say. Pentagon and military experts say such tactics can threaten to alter the course of the war and the effectiveness of the surge.
Mackenzie Eaglen, a military analyst at the Heritage Foundation, says insurgents hope mounting casualties during the coalition offensive will demoralize troops and erode public and political support for the war at home.
"They're after headlines," Eaglen says. They hope "to influence the international narrative of what's happening in Afghanistan."
A recently released report by the Pentagon's Joint IED Defeat Organization (JIEDDO) identified IEDs as "the most serious threat" to coalition forces. Roadside bombs wounded or killed 6,200 allied troops and Afghan forces in fiscal year 2009 compared with 3,800 in 2008. Casualties are even higher this year.
In Helmand province alone, 272 IEDs exploded and 231 were found and cleared in the month of August. Nine troops were killed and 148 wounded. The surge "has led to the highest rate of IED attacks on (coalition troops) since the conflict began in 2001," according to the Pentagon report.
Because the bombs cause such carnage on a daily basis, they must be neutralized, JIEDDO says.
Manning's battalion has suffered more IED attacks than any other Marine battalion in the province. He lost a dozen Marines in six months, nine killed by bombs, including two explosives experts and an engineer who died trying to disarm the devices. Fifteen of his Marines lost limbs. The threat is on the minds of U.S. servicemembers.
"That's what gives me the biggest headache is wondering if I should walk around. Staring at the ground. Going cross-eyed over it," Marine Sgt. Jason Westenkow says.
At an outpost outside the village of Kunjak, Marine Sgt. John Ellis, 26, squad leader, holds up a yellow, 5-gallon jug, the type used routinely for chores in any Afghan home or merchant shop. "This is what they use for IEDs," he says.
The jugs are filled with 15 to 40 pounds of explosives and can be stuffed with ball bearings, nuts, bolts and screws for shrapnel. They are fitted with a simple pressure-plate detonator constructed of two pieces of plastic-wrapped wood sandwiching electric wire, Ellis says.
Bombs are set off remotely by radio or triggered from the end of a wire. The fine dust that powders roads and dry riverbed crossings conceals pressure plates. Lush irrigated fields are ripe for tripwires. Many armored trucks have been damaged or disabled by the bombs.
The first line of defense for a foot patrol is the metal detector. Lance Cpl. Matthew Dickens, 20, slowly swings the device back and forth searching for a signal.
He has found half a dozen bombs listening for the beep that becomes more rapid when the detector is over an explosive. Dickens then lies on his stomach, his heart pounding, and slowly uncovers enough earth to reveal whether a bomb is there.
He tries not to think about what might happen. "It if goes off, you're probably not going to feel a lot of anything. You'll just be done," he says. "Afterward, it's relief knowing that I'm away from it. It's not going to blow me up."