Even after cutting off the head of al-Qaeda, the United States Department of Defense doesn’t believe an end to the war on terror is in sight. On Thursday, one Pentagon official predicted the mission against al-Qaeda could continue for another two decades.

Speaking to the Senate Armed Services early Thursday, Assistant Secretary of Defense for Special Operations Michael Sheehan said the Pentagon has no plans to pull out of its almost 12-year-old war overseas.

When asked for his take on how long the war on terror could go on for, Sheehan told lawmakers, “At least 10 to 20 years.”

According to US President Barack Obama, the last combat troops will move out of Afghanistan in 2014. If remarks from Sheehan and others are at all accurate, though, in reality the war could last through the 2030s.

Sheehan was being grilled by members of the Senate committee on Thursday over not just the future of the war, but what rules are in play to continue the operation. Congress granted then-President George W. Bush the power to go after al-Qaeda in 2001 by signing the Authorization to Use Military Force, a legislation that essentially gave the go-ahead to use America’s might by any means necessary to avenge the attacks of 9/11. Nearly 13 years later, though, some members of the Senate saw that the overly broad powers extended to the commander-in-chief through the AUMF are being used to justify a widening war that now has soldiers targeting insurgents in venue like Yemen and Somalia.

The scope of America’s counterterrorism program, Sheehan said, stretches “from Boston to the FATA,” referring to the region of Pakistan considered a hotbed of terrorism. Because of that widening arena, some senators said it’s time to rewrite the law.

“It has spread throughout North Africa, throughout the Maghreb,” Senator John McCain (R-Arizona) said during the hearing. “The situation’s changed dramatically.

But while some lawmakers suggested it was time to revise the AUMF, Pentagon officials said the 2012 National Defense Authorization Act updated the law to grant the president power not just to target overseas terrorists, but suspects believed to be associated forces.

Robert Taylor, the acting general counsel of the Department of Defense, said that the NDAA’s update to the Bush-era bill means that even suspects born after the September 11 attacks could be targeted as warriors in the war on terror.

“As long as they become an associated force under the legal standard that was set out,” Taylor testified, according to Wired’s Spencer Ackermnn.

Sen. Angus King, an Independent from Maine, suggested the Pentagon was uninterested in changing the AUMF because they are using it to justify a war that wouldn’t otherwise be legal.

“This is the most disturbing hearing I’ve been to in some time,” King said. “You guys have rewritten the Constitution today.”

“You guys have invented this term, associated forces, that’s nowhere in this document,” King said. “It’s the justification for everything, and it renders the war powers of Congress null and void.”

“I assume [the AUMF] does suit you well because you’re reading it to fit everything, and it doesn’t, the general rule of war applies,” King said.

Even McCain, who has been by and large considered a hawkish member of the Senate, spoke out against the Pentagon’s reluctance to re-write a law that they are using to justify a war that could take US troops to all corners of the globe for the unforeseeable future.

“For you to come here and say, ‘We don’t need to change it,’ I think, is disturbing,” McCain said.

Before stepping down as secretary of defense, former Pentagon chief Leon Panetta said in late 2011, “We're winning this very tough conflict.” Osama bin Laden was executed five months later, and the Central Intelligence Agency and DoD have continuously utilized strikes to weaken al-Qaeda substantially since.