WASHINGTON -- After an emotional debate over how to keep Americans safe, the Senate Thursday narrowly defeated an effort to prevent civilian trials in U.S. courts for the accused planners of the 9/11 attacks.

The Senate's 54-45 vote to reject the measure by Sen. Lindsey Graham, R-S.C., opens the door for President Barack Obama to bring Khalid Sheik Mohammed, the self-professed mastermind of the Sept. 11, 2001, attacks, to trial in federal courts, rather than the military commissions Graham helped create.

Obama has pledged to shutter the U.S. military prison at Guantanamo Bay, Cuba, by January and transfer some of its 220 detainees to the U.S. for trials in civilian courts.

Three Democrats - Jim Webb of Virginia and Arkansas' Blanche Lincoln and Mark Pryor - and independent Joe Lieberman of Connecticut joined all 40 Senate Republicans in voting for the measure.

Graham, a military lawyer who has served active duty in the Iraq and Afghanistan wars, pleaded with his colleagues to back his amendment to a spending measure for the Justice Department and other federal agencies.

"Tell the president that we're not going to sit by as a body and watch the mastermind of 9/11 go into civilian court and criminalize this war," Graham said. "If he goes to federal court, here's what awaits - a chaos zoo trial."