US Marines swear an oath to “support and defend the Constitution of the United States against all enemies, foreign and domestic…”

After Scott Olsen swore that oath in 2006, he served two tours of duty in Iraq before being discharged in 2010.

Olsen survived Iraq. But he was seriously wounded Tuesday when he joined an Oakland, California, protest against the removal of the Occupy Wall Street–inspired encampment in that Bay Area city. The clashes between activists and the Oakland Police turned violent late Tuesday, during what the San Francisco Chronicle described as “a protracted street confrontation between protesters and police officers, who set off tear gas and used shotguns to fire projectiles designed to inflict pain but not kill.”

The precise number of injuries is unclear. But Oakland’s Highland Hospital confirmed Wednesday that Olsen, 24, was in serious condition.

Olsen, who now works as a system administrator for a software firm, had joined the Oakland protests with fellow members of Iraq Veterans Against the War, an advocacy group that has long sought to draw attention to issues of homelessness and unemployment among Americans who served in Iraq and Afghanistan. According to Keith Shannon, who deployed with Olsen to Iraq, “Scott was marching with the 99 percent because he felt corporations and banks had too much control over our government, and that they weren’t being held accountable for their role in the economic downturn, which caused so many people to lose their jobs and their homes.”

IVAW’s reports from the scene—along with agonizing video footage that features cries of “medic!”—suggest that Olsen “sustained a skull fracture after being shot in the head with a police projectile while peacefully participating in an Occupy Oakland march.”

The video footage of appears to show Olsen lying wounded when a police officer what looks to be a tear gas canister at protesters who are trying to help the former Marine.

IVAW, which is demanding that Oakland Mayor Jean Quan investigate the incident and allow peaceful protests to continue, featured a statement on its website Wednesday night that read: “It’s ironic that days after Obama’s announcement of the end of the Iraq War, Scott faced a veritable war zone in the streets of Oakland last night. He and other protesters were surrounded by explosions and smoke (tear gas) going off around him as people nearby carried him injured while yelling for a medic. This disturbing video of the incident shows how veterans are now fighting a war at home.”

In fact, it’s not so ironic. Returning veterans who have sought to exercise their rights at home have, at many points in American history, been the victims of violence—especially when they have made demands of Wall Street. When a “Bonus Army” consisting of thousands of World War I veterans camped near the Capitol in Washington, DC, in the summer of 1932—demanding payment of bonuses they had been promised for their service, and that they needed to survive in those Depression Days—they were attacked first by the police and then by the US Army,

Two veterans were killed. One of them, Eric Carlson, was from Oakland, California.

The revulsion at the attacks on the veterans in 1932 would eventually lead to a decision by the Congress of $2 billion to pay immediate bonuses to the World War I veterans.

Retired Major General Smedley Darlington Butler, a two-time recipient of the Congressional Medal of Honor, joined the Bonus Army at its encampment and supported its demands. Bulter is today remembered for his epic denunciation of the military-industrial complex:

I spent 33 years and four months in active military service and during that period I spent most of my time as a high class thug for Big Business, for Wall Street and the bankers. In short, I was a racketeer, a gangster for capitalism. I helped make Mexico and especially Tampico safe for American oil interests in 1914. I helped make Haiti and Cuba a decent place for the National City Bank boys to collect revenues in. I helped in the raping of half a dozen Central American republics for the benefit of Wall Street. I helped purify Nicaragua for the International Banking House of Brown Brothers in 1902–1912. I brought light to the Dominican Republic for the American sugar interests in 1916. I helped make Honduras right for the American fruit companies in 1903. In China in 1927 I helped see to it that Standard Oil went on its way unmolested. Looking back on it, I might have given Al Capone a few hints. The best he could do was to operate his racket in three districts. I operated on three continents.

But after the attack on the Bonus Army, he issued an even blunter declaration, announcing in 1933 that: “I believe in…taking Wall St. by the throat and shaking it up.”

Today’s Occupy Wall Street protests are, perhaps, less aggressive than those that came before. But the veterans who join today’s protests are being met with the same violence—and disrespect—that the Bonus Army experienced.

“I think it is a sad state of affairs when a Marine can’t assemble peacefully in the streets without getting injured,” says Jose Sanchez, the executive director of Iraq Veterans Against the War.

Major General Smedley Butler would surely agree.