The U.S. Senate approved an amendment on Thursday that strips a controversial provision from the 2012 National Defense Authorization Act that allows the "indefinite detention" of American citizens within the U.S. by the military.

The amendment passed by a vote of 67 to 29. All but four of the Senators who voted against civilian trials for Americans were Republicans. Sens. Joe Manchin (D-WV), Ben Nelson (D-NE) and Mark Pryor (D-AR) crossed over to oppose the amendment, and they were joined by Joe Lieberman (I-CT).

The amendment reads: "An authorization to use military force, a declaration of war, or any similar authority shall not authorize the detention without charge or trial of a citizen or lawful permanent resident of the United States apprehended in the United States, unless an Act of Congress expressly authorizes such detention."

A similar amendment put forward by Sen. Dianne Feinstein (D-CA) in 2011 failed to clear the Senate by a vote of 45 to 55. In that vote, 11 Democrats crossed over to oppose civilian trials for American citizens.

The 2011 NDAA was signed by a reluctant President Barack Obama, who added a signing statement explaining that his administration would not allow Americans to be detained by the military without access to a speedy trial, as guaranteed by the U.S. Constitution. Critics warned, however, that allowing the provision to remain codified in law could spell disaster during some future administration. Even so, Republicans threatened to sink the bill, which authorizes the annual military budget, if the "indefinite detention" language was not kept intact.

This year, things are shaping up differently. Fresh off his successful reelection bid, President Obama said Thursday that he will veto the NDAA if Congress keeps additional language in the bill that prevents him from transferring military prisoners into civilian custody. That language in the 2011 bill effectively blocks the president from closing down Guantanamo Bay, the military prison where 166 so-called "terror war" prisoners from the Bush-era remain today.

A Government Accountability Office report requested by Sen. Feinstein and released earlier this week says that the Department of Defense and the Department of Justice have more than enough secure prison space inside the U.S. to house the remaining Guantanamo Bay prisoners without concern for safety. A total of 377 inmates who've been charged with or convicted of terrorism are already residing in U.S. prisons, the report noted.

"The beauty of our Constitution is that it gives everyone in the United States basic due process rights to a trial by a jury of their peers," Feinstein said, speaking Thursday on the floor of the Senate. "That is what makes this nation great... The federal government experimented with indefinite detention of United States citizens during World War II, a mistake we now recognize as a betrayal of our core values. Let's not repeat it."

Despite Feinstein's reference to World War II -- which saw the U.S. send thousands of Japanese citizens and Japanese-Americans into internment camps without charge or trial -- the American Civil Liberties Union noted that the Feinstein amendment doesn't make an exception for non-citizens and other immigrants who aren't "lawful permanent residents," which could set a bad precedent.

"It is inconsistent with the Constitution, which makes clear that basic due process rights apply to everyone in the United States," ACLU's Chris Anders wrote. "No group of immigrants should be denied the most basic due process right of all -- the right to be charged and tried before being imprisoned."


Updated for context and to add a quote.